Schedule and automate LinkedIn posts with Zernio API - Personal profiles, company pages, images, videos, documents, and multi-organization posting

Quick Reference

Property	Value
Character limit	3,000
Images per post	20
Videos per post	1
Documents per post	1 (PDF, PPT, PPTX, DOC, DOCX)
Image formats	JPEG, PNG, GIF
Image max size	8 MB
Video formats	MP4, MOV, AVI
Video max size	5 GB
Video max duration	10 min (personal), 30 min (company page)
Post types	Text, Image, Multi-image, Video, Document
Scheduling	Yes
Inbox (Comments)	Yes (add-on, company pages only)
Inbox (DMs)	No (LinkedIn blocks third-party DM access)
Analytics	Yes

LinkedIn actively suppresses posts containing external links. Your post's organic reach can drop 40-50% if you include a URL in the caption. Best practice: put your link in the first comment using the firstComment field. Also: LinkedIn rejects duplicate content with a 422 error. You cannot post the same text twice, even across different time periods.

Additional details:

Works with personal profiles AND company pages
Company pages: full analytics, 30-min video, comments API
Personal profiles: limited analytics, 10-min video
Cannot mix media types (images + videos or images + documents in the same post)
First ~210 characters of your post are visible before the "see more" fold

Quick Start

Post to LinkedIn in under 60 seconds:

const { post } = await zernio.posts.createPost({
  content: 'Excited to share our latest update!\n\nWe have been working hard on this feature...',
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Excited to share our latest update!\n\nWe have been working hard on this feature...",
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Excited to share our latest update!\n\nWe have been working hard on this feature...",
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Content Types

Text-Only Post

Text posts get the highest organic reach on LinkedIn. The first ~210 characters appear before the "see more" fold, so lead with your hook. Up to 3,000 characters total.

const { post } = await zernio.posts.createPost({
  content: 'I spent 3 years building the wrong product.\n\nHere is what I learned about validating ideas before writing code...',
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="I spent 3 years building the wrong product.\n\nHere is what I learned about validating ideas before writing code...",
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "I spent 3 years building the wrong product.\n\nHere is what I learned about validating ideas before writing code...",
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Single Image Post

Attach one image to a post. Recommended size is 1200 x 627 px (landscape).

const { post } = await zernio.posts.createPost({
  content: 'Our new office setup is looking great!',
  mediaItems: [
    { type: 'image', url: 'https://cdn.example.com/office.jpg' }
  ],
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Our new office setup is looking great!",
    media_items=[
        {"type": "image", "url": "https://cdn.example.com/office.jpg"}
    ],
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Our new office setup is looking great!",
    "mediaItems": [
      {"type": "image", "url": "https://cdn.example.com/office.jpg"}
    ],
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Multi-Image Post

LinkedIn supports up to 20 images in a single post. Cannot include videos or documents alongside images.

const { post } = await zernio.posts.createPost({
  content: 'Highlights from our team retreat!',
  mediaItems: [
    { type: 'image', url: 'https://cdn.example.com/photo1.jpg' },
    { type: 'image', url: 'https://cdn.example.com/photo2.jpg' },
    { type: 'image', url: 'https://cdn.example.com/photo3.jpg' }
  ],
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Highlights from our team retreat!",
    media_items=[
        {"type": "image", "url": "https://cdn.example.com/photo1.jpg"},
        {"type": "image", "url": "https://cdn.example.com/photo2.jpg"},
        {"type": "image", "url": "https://cdn.example.com/photo3.jpg"}
    ],
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Highlights from our team retreat!",
    "mediaItems": [
      {"type": "image", "url": "https://cdn.example.com/photo1.jpg"},
      {"type": "image", "url": "https://cdn.example.com/photo2.jpg"},
      {"type": "image", "url": "https://cdn.example.com/photo3.jpg"}
    ],
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Video Post

One video per post. Personal profiles support up to 10 minutes, company pages up to 30 minutes. MP4, MOV, and AVI formats. GIFs are converted to video and count against the 1-video limit.

const { post } = await zernio.posts.createPost({
  content: 'Watch our latest product demo',
  mediaItems: [
    { type: 'video', url: 'https://cdn.example.com/demo.mp4' }
  ],
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Watch our latest product demo",
    media_items=[
        {"type": "video", "url": "https://cdn.example.com/demo.mp4"}
    ],
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Watch our latest product demo",
    "mediaItems": [
      {"type": "video", "url": "https://cdn.example.com/demo.mp4"}
    ],
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Document/Carousel Post

LinkedIn uniquely supports document uploads (PDF, PPT, PPTX, DOC, DOCX) that display as swipeable carousels. Max 100 MB, up to 300 pages. Cannot include images or videos alongside a document.

const { post } = await zernio.posts.createPost({
  content: 'Download our 2024 Industry Report',
  mediaItems: [
    { type: 'document', url: 'https://cdn.example.com/report.pdf' }
  ],
  platforms: [
    { platform: 'linkedin', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Download our 2024 Industry Report",
    media_items=[
        {"type": "document", "url": "https://cdn.example.com/report.pdf"}
    ],
    platforms=[
        {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Download our 2024 Industry Report",
    "mediaItems": [
      {"type": "document", "url": "https://cdn.example.com/report.pdf"}
    ],
    "platforms": [
      {"platform": "linkedin", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Document tips:

First page is the cover/preview -- design it to grab attention
Design for mobile viewing (large fonts, minimal text per slide)
Ideal length for engagement: 10-15 pages
Password-protected PDFs will not work

Media Requirements

Images

Property	Requirement
Max images	20 per post
Formats	JPEG, PNG, GIF
Max file size	8 MB per image
Recommended	1200 x 627 px
Min dimensions	552 x 276 px
Max dimensions	8192 x 8192 px

Aspect Ratios

Type	Ratio	Dimensions	Use Case
Landscape	1.91:1	1200 x 627 px	Link shares, standard
Square	1:1	1080 x 1080 px	Engagement
Portrait	1:1.25	1080 x 1350 px	Mobile feed

Videos

Property	Requirement
Max videos	1 per post
Formats	MP4, MOV, AVI
Max file size	5 GB
Max duration	10 min (personal), 30 min (company page)
Min duration	3 seconds
Resolution	256 x 144 px to 4096 x 2304 px
Aspect ratio	1:2.4 to 2.4:1
Frame rate	10-60 fps

Documents

Property	Requirement
Max documents	1 per post
Formats	PDF, PPT, PPTX, DOC, DOCX
Max file size	100 MB
Max pages	300 pages

Platform-Specific Fields

All fields go inside platformSpecificData on the LinkedIn platform entry.

Field	Type	Description
`documentTitle`	string	Title displayed on LinkedIn document (PDF/carousel) posts. Required by LinkedIn for document posts. If omitted, falls back to the media item `title`, then the `filename`.
`organizationUrn`	string	Post to a specific LinkedIn company page. Format: `urn:li:organization:123456`. Get available orgs via `GET /v1/accounts/{accountId}/linkedin-organizations`. If omitted, posts to default org or personal profile.
`firstComment`	string	Auto-posted as first comment after publish. Best practice: put external links here since LinkedIn suppresses link posts by 40-50%.
`disableLinkPreview`	boolean	Set to `true` to suppress the automatic URL preview card. Default: `false`.

LinkedIn Document Titles

LinkedIn requires a title for document (PDF/carousel) posts. Set platformSpecificData.documentTitle to control the title shown on LinkedIn.

Note: If documentTitle is omitted, Zernio falls back to the media item title, then the filename.

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Download our 2024 Industry Report",
    "mediaItems": [
      {"type": "document", "url": "https://cdn.example.com/report.pdf"}
    ],
    "platforms": [{
      "platform": "linkedin",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "documentTitle": "2024 Industry Report"
      }
    }],
    "publishNow": true
  }'

const { post } = await zernio.posts.createPost({
  content: 'Download our 2024 Industry Report',
  mediaItems: [
    { type: 'document', url: 'https://cdn.example.com/report.pdf' }
  ],
  platforms: [{
    platform: 'linkedin',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      documentTitle: '2024 Industry Report'
    }
  }],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Download our 2024 Industry Report",
    media_items=[
        {"type": "document", "url": "https://cdn.example.com/report.pdf"}
    ],
    platforms=[{
        "platform": "linkedin",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "documentTitle": "2024 Industry Report"
        }
    }],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

Multi-Organization Posting

If your connected LinkedIn account manages multiple organizations (company pages), you can post to different organizations from the same account connection.

List available organizations:

const organizations = await zernio.accounts.getLinkedInOrganizations('YOUR_ACCOUNT_ID');
console.log('Available organizations:', organizations);

organizations = client.accounts.get_linkedin_organizations("YOUR_ACCOUNT_ID")
print("Available organizations:", organizations)

curl -X GET https://zernio.com/api/v1/accounts/YOUR_ACCOUNT_ID/linkedin-organizations \
  -H "Authorization: Bearer YOUR_API_KEY"

Post to multiple organizations using the same accountId with different organizationUrn values:

const { post } = await zernio.posts.createPost({
  content: 'Exciting updates from our organization!',
  platforms: [
    {
      platform: 'linkedin',
      accountId: 'YOUR_ACCOUNT_ID',
      platformSpecificData: { organizationUrn: 'urn:li:organization:111111111' }
    },
    {
      platform: 'linkedin',
      accountId: 'YOUR_ACCOUNT_ID',
      platformSpecificData: { organizationUrn: 'urn:li:organization:222222222' }
    }
  ],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Exciting updates from our organization!",
    platforms=[
        {
            "platform": "linkedin",
            "accountId": "YOUR_ACCOUNT_ID",
            "platformSpecificData": {"organizationUrn": "urn:li:organization:111111111"}
        },
        {
            "platform": "linkedin",
            "accountId": "YOUR_ACCOUNT_ID",
            "platformSpecificData": {"organizationUrn": "urn:li:organization:222222222"}
        }
    ],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Exciting updates from our organization!",
    "platforms": [
      {
        "platform": "linkedin",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
          "organizationUrn": "urn:li:organization:111111111"
        }
      },
      {
        "platform": "linkedin",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
          "organizationUrn": "urn:li:organization:222222222"
        }
      }
    ],
    "publishNow": true
  }'

The organizationUrn format is urn:li:organization: followed by the organization ID.

First Comment

Put external links in the first comment to avoid LinkedIn's link suppression algorithm:

const { post } = await zernio.posts.createPost({
  content: 'We just published our guide to API design patterns.\n\nLink in the first comment.',
  platforms: [{
    platform: 'linkedin',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      firstComment: 'Read the full guide here: https://example.com/api-guide'
    }
  }],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="We just published our guide to API design patterns.\n\nLink in the first comment.",
    platforms=[{
        "platform": "linkedin",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "firstComment": "Read the full guide here: https://example.com/api-guide"
        }
    }],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "We just published our guide to API design patterns.\n\nLink in the first comment.",
    "platforms": [{
      "platform": "linkedin",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "firstComment": "Read the full guide here: https://example.com/api-guide"
      }
    }],
    "publishNow": true
  }'

Disable Link Preview

When posting text with URLs and no media, LinkedIn auto-generates a link preview card. To suppress it:

const { post } = await zernio.posts.createPost({
  content: 'Check out our latest blog post! https://example.com/blog/new-post',
  platforms: [{
    platform: 'linkedin',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      disableLinkPreview: true
    }
  }],
  publishNow: true
});
console.log('Posted to LinkedIn!', post._id);

result = client.posts.create(
    content="Check out our latest blog post! https://example.com/blog/new-post",
    platforms=[{
        "platform": "linkedin",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "disableLinkPreview": True
        }
    }],
    publish_now=True
)
post = result.post
print(f"Posted to LinkedIn! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Check out our latest blog post! https://example.com/blog/new-post",
    "platforms": [{
      "platform": "linkedin",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "disableLinkPreview": true
      }
    }],
    "publishNow": true
  }'

Media URL Requirements

These do not work as media URLs:

Google Drive -- returns an HTML download page, not the file
Dropbox -- returns an HTML preview page
OneDrive / SharePoint -- returns HTML
iCloud -- returns HTML

Test your URL in an incognito browser window. If you see a webpage instead of the raw image or video, it will not work.

Media URLs must be:

Publicly accessible (no authentication required)
Returning actual media bytes with the correct Content-Type header
Not behind redirects that resolve to HTML pages
Hosted on a fast, reliable CDN

Supabase URLs: Zernio auto-proxies Supabase storage URLs, so they work without additional configuration.

Analytics

Requires Analytics add-on

Available metrics via the Analytics API:

Metric	Available
Impressions	✅
Reach	✅
Likes	✅
Comments	✅
Shares	✅
Clicks	✅
Views	✅ (video posts only)

LinkedIn also provides dedicated analytics endpoints for deeper insights:

Aggregate Analytics -- Organization-level totals or daily time series across all posts
Post Analytics -- Per-post metrics by URN
Post Reactions -- Individual reactions with reactor profiles (organization accounts only)

const analytics = await zernio.analytics.getAnalytics({
  platform: 'linkedin',
  fromDate: '2024-01-01',
  toDate: '2024-01-31'
});
console.log(analytics.posts);

analytics = client.analytics.get(
    platform="linkedin",
    from_date="2024-01-01",
    to_date="2024-01-31"
)
print(analytics["posts"])

curl "https://zernio.com/api/v1/analytics?platform=linkedin&fromDate=2024-01-01&toDate=2024-01-31" \
  -H "Authorization: Bearer YOUR_API_KEY"

What You Can't Do

These features are not available through LinkedIn's API:

Publish long-form articles (linkedin.com/article/new/)
Create polls
Create events
Send InMail or DMs
Create newsletters
Boost or promote posts
Add reactions to other posts
Create hashtag-following or tag connections
Mix media types (images + videos or images + documents in the same post)
Post GIFs as images (GIFs are converted to video and count as video)

Common Errors

LinkedIn has a 9.5% failure rate across Zernio's platform (8,082 failures out of 85,512 attempts). Here are the most frequent errors and how to fix them:

Error	What it means	How to fix
"Content is a duplicate of urn:li:share:XXXX" (422)	Identical or very similar content was already posted	Modify the text meaningfully. LinkedIn's duplicate detection is strict -- even minor rephrasing may not be enough.
"Publishing failed during preflight checks"	Rate limiting or validation caught an issue before publishing	Space posts further apart. Check account health in the dashboard.
"Publishing failed due to max retries reached"	All 3 retry attempts failed	Temporary issue. Retry manually or check LinkedIn's status page.
Token expired	OAuth access token has expired or been revoked	Reconnect the LinkedIn account. Subscribe to the `account.disconnected` webhook to catch this proactively.
"Cannot mix media types"	Post contains images + videos or images + documents	Use only one media type per post. GIFs count as video.
Video processing failed	Codec, duration, or aspect ratio is out of spec	Ensure codec is H.264, duration is within limits (10 min personal / 30 min company), and aspect ratio is between 1:2.4 and 2.4:1.
Link preview showing wrong image	Open Graph meta tags on the URL are incorrect or missing	Update the `og:image` tag on your website. LinkedIn caches previews -- use the LinkedIn Post Inspector to refresh.

Inbox

Requires Inbox add-on — Build: +$10/mo · Accelerate: +$50/unit · Unlimited: +$1,000/mo

LinkedIn supports comments only (no DMs via API).

Comments

Feature	Supported
List comments on posts	✅
Reply to comments	✅
Delete comments	✅
Like comments	❌ (API restricted)

Limitations

No DMs - LinkedIn's messaging API is not available for third-party apps
Organization accounts only - Comments require an organization (company page) account type
No comment likes - Liking/reacting to comments via API is restricted. However, you can read post reactions via GET /v1/accounts/{accountId}/linkedin-post-reactions (organization accounts only).

See Comments API Reference for endpoint details.

Connect LinkedIn Account - OAuth flow
Create Post - Post creation and scheduling
Upload Media - Image and video uploads
LinkedIn Organizations - List company pages
LinkedIn Mentions - Track brand mentions
LinkedIn Aggregate Analytics - Organization-level analytics
LinkedIn Post Analytics - Post-level performance metrics
LinkedIn Post Reactions - Who reacted to a post (organization accounts)
Comments - Inbox API