Schedule and automate Facebook Page posts with Zernio API - Feed posts, Stories, multi-image, GIFs, and first comments

Quick Reference

Property	Value
Character limit	63,206 (truncated at ~480 with "See more")
Images per post	10
Videos per post	1
Image formats	JPEG, PNG, GIF (WebP auto-converted to JPEG)
Image max size	4 MB (Facebook rejects larger in practice)
Video formats	MP4, MOV
Video max size	4 GB
Video max duration	240 min (feed), 120 sec (stories)
Post types	Feed (text/image/video/multi-image), Story
Scheduling	Yes
Inbox (DMs)	Yes (add-on)
Inbox (Comments)	Yes (add-on)
Inbox (Reviews)	Yes (add-on)
Analytics	Yes

Facebook API only posts to Pages, not personal profiles. You must have a Facebook Page and admin access to it. Also: Facebook often rejects photos larger than 4 MB even though the stated limit is higher. Keep images under 4 MB and use JPEG or PNG format. WebP images are auto-converted to JPEG by Zernio.

API posts to Pages only (not personal profiles)
User must be Page Admin or Editor
Facebook tokens expire frequently -- subscribe to the account.disconnected webhook
Multiple Pages can be managed from one connected account

Quick Start

Post to a Facebook Page in under 60 seconds:

const { post } = await zernio.posts.createPost({
  content: 'Hello from Zernio API!',
  platforms: [
    { platform: 'facebook', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});
console.log('Posted to Facebook!', post._id);

result = client.posts.create(
    content="Hello from Zernio API!",
    platforms=[
        {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)
post = result.post
print(f"Posted to Facebook! {post['_id']}")

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Hello from Zernio API!",
    "platforms": [
      {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Content Types

Text-Only Post

No media required. Facebook is one of the few platforms that supports text-only posts.

const { post } = await zernio.posts.createPost({
  content: 'Just a text update for our followers.',
  platforms: [
    { platform: 'facebook', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});

result = client.posts.create(
    content="Just a text update for our followers.",
    platforms=[
        {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Just a text update for our followers.",
    "platforms": [
      {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Single Image Post

const { post } = await zernio.posts.createPost({
  content: 'Check out this photo!',
  mediaItems: [
    { type: 'image', url: 'https://example.com/photo.jpg' }
  ],
  platforms: [
    { platform: 'facebook', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});

result = client.posts.create(
    content="Check out this photo!",
    media_items=[
        {"type": "image", "url": "https://example.com/photo.jpg"}
    ],
    platforms=[
        {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Check out this photo!",
    "mediaItems": [
      {"type": "image", "url": "https://example.com/photo.jpg"}
    ],
    "platforms": [
      {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Multi-Image Post

Facebook supports up to 10 images in a single post. You cannot mix images and videos in the same post.

const { post } = await zernio.posts.createPost({
  content: 'Photo dump from the weekend!',
  mediaItems: [
    { type: 'image', url: 'https://example.com/photo1.jpg' },
    { type: 'image', url: 'https://example.com/photo2.jpg' },
    { type: 'image', url: 'https://example.com/photo3.jpg' }
  ],
  platforms: [
    { platform: 'facebook', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});

result = client.posts.create(
    content="Photo dump from the weekend!",
    media_items=[
        {"type": "image", "url": "https://example.com/photo1.jpg"},
        {"type": "image", "url": "https://example.com/photo2.jpg"},
        {"type": "image", "url": "https://example.com/photo3.jpg"}
    ],
    platforms=[
        {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)

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

Video Post

A single video per post. For GIFs, use type: 'video' -- they are treated as videos internally, auto-play, and loop.

const { post } = await zernio.posts.createPost({
  content: 'Watch our latest video!',
  mediaItems: [
    { type: 'video', url: 'https://example.com/video.mp4' }
  ],
  platforms: [
    { platform: 'facebook', accountId: 'YOUR_ACCOUNT_ID' }
  ],
  publishNow: true
});

result = client.posts.create(
    content="Watch our latest video!",
    media_items=[
        {"type": "video", "url": "https://example.com/video.mp4"}
    ],
    platforms=[
        {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    publish_now=True
)

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 video!",
    "mediaItems": [
      {"type": "video", "url": "https://example.com/video.mp4"}
    ],
    "platforms": [
      {"platform": "facebook", "accountId": "YOUR_ACCOUNT_ID"}
    ],
    "publishNow": true
  }'

Story (Image or Video)

Stories are 24-hour ephemeral content. Media is required. Text captions are not displayed on Stories, and interactive stickers are not supported via the API.

const { post } = await zernio.posts.createPost({
  mediaItems: [
    { type: 'image', url: 'https://example.com/story.jpg' }
  ],
  platforms: [{
    platform: 'facebook',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      contentType: 'story'
    }
  }],
  publishNow: true
});

result = client.posts.create(
    media_items=[
        {"type": "image", "url": "https://example.com/story.jpg"}
    ],
    platforms=[{
        "platform": "facebook",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "contentType": "story"
        }
    }],
    publish_now=True
)

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "mediaItems": [
      {"type": "image", "url": "https://example.com/story.jpg"}
    ],
    "platforms": [{
      "platform": "facebook",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "contentType": "story"
      }
    }],
    "publishNow": true
  }'

Reel (Video)

Publish a Facebook Reel (short vertical video). Reels require a single vertical video.

Note: content is used as the Reel caption. Use platformSpecificData.title to set a separate Reel title.

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Behind the scenes 🎬",
    "mediaItems": [
      {"type": "video", "url": "https://example.com/reel.mp4"}
    ],
    "platforms": [{
      "platform": "facebook",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "contentType": "reel",
        "title": "Studio day"
      }
    }],
    "publishNow": true
  }'

const { post } = await zernio.posts.createPost({
  content: 'Behind the scenes 🎬',
  mediaItems: [
    { type: 'video', url: 'https://example.com/reel.mp4' }
  ],
  platforms: [{
    platform: 'facebook',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      contentType: 'reel',
      title: 'Studio day'
    }
  }],
  publishNow: true
});
console.log('Posted Reel to Facebook!', post._id);

result = client.posts.create(
    content="Behind the scenes 🎬",
    media_items=[
        {"type": "video", "url": "https://example.com/reel.mp4"}
    ],
    platforms=[{
        "platform": "facebook",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "contentType": "reel",
            "title": "Studio day"
        }
    }],
    publish_now=True
)
post = result.post
print(f"Posted Reel to Facebook! {post['_id']}")

Reel requirements

Single video only (no images)
Vertical video recommended (9:16)
Duration: 3–60 seconds

First Comment

Auto-post a first comment immediately after your post is published. Does not work with Stories or Reels.

const { post } = await zernio.posts.createPost({
  content: 'New product launch!',
  mediaItems: [
    { type: 'image', url: 'https://example.com/product.jpg' }
  ],
  platforms: [{
    platform: 'facebook',
    accountId: 'YOUR_ACCOUNT_ID',
    platformSpecificData: {
      firstComment: 'Link to purchase: https://shop.example.com'
    }
  }],
  publishNow: true
});

result = client.posts.create(
    content="New product launch!",
    media_items=[
        {"type": "image", "url": "https://example.com/product.jpg"}
    ],
    platforms=[{
        "platform": "facebook",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
            "firstComment": "Link to purchase: https://shop.example.com"
        }
    }],
    publish_now=True
)

curl -X POST https://zernio.com/api/v1/posts \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "New product launch!",
    "mediaItems": [
      {"type": "image", "url": "https://example.com/product.jpg"}
    ],
    "platforms": [{
      "platform": "facebook",
      "accountId": "YOUR_ACCOUNT_ID",
      "platformSpecificData": {
        "firstComment": "Link to purchase: https://shop.example.com"
      }
    }],
    "publishNow": true
  }'

Media Requirements

Images

Property	Feed Post	Story
Max images	10	1
Formats	JPEG, PNG, GIF (WebP auto-converted)	JPEG, PNG
Max file size	4 MB	4 MB
Recommended	1200 x 630 px	1080 x 1920 px

Videos

Property	Feed Video	Story
Max videos	1	1
Formats	MP4, MOV	MP4, MOV
Max file size	4 GB	4 GB
Max duration	240 minutes	120 seconds
Min duration	1 second	1 second
Recommended resolution	1280 x 720 px min	1080 x 1920 px
Frame rate	30 fps recommended	30 fps
Codec	H.264	H.264

Platform-Specific Fields

All fields below go inside platformSpecificData for the Facebook platform entry.

Field	Type	Description
`contentType`	`"story"` \| `"reel"`	Set to `"story"` for Page Stories (24h ephemeral) or `"reel"` for Reels (short vertical video). Defaults to feed post if omitted.
`title`	string	Reel title (only for `contentType="reel"`). Separate from the `content` caption.
`firstComment`	string	Auto-posted as the first comment after publish. Feed posts only (not Stories or Reels).
`pageId`	string	Post to a specific Page when the connected account manages multiple Pages. Get available pages with `GET /v1/accounts/{accountId}/facebook-page`.

Multi-Page Posting

If your connected Facebook account manages multiple Pages, you can list them, set a default, or override per post.

List Available Pages

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

pages = client.accounts.get_facebook_page("YOUR_ACCOUNT_ID")
print("Available pages:", pages)

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

Post to Multiple Pages

Use the same accountId multiple times with different pageId values:

const { post } = await zernio.posts.createPost({
  content: 'Exciting news from all our brands!',
  platforms: [
    {
      platform: 'facebook',
      accountId: 'YOUR_ACCOUNT_ID',
      platformSpecificData: { pageId: '111111111' }
    },
    {
      platform: 'facebook',
      accountId: 'YOUR_ACCOUNT_ID',
      platformSpecificData: { pageId: '222222222' }
    }
  ],
  publishNow: true
});
console.log('Posted to Facebook!', post._id);

result = client.posts.create(
    content="Exciting news from all our brands!",
    platforms=[
        {
            "platform": "facebook",
            "accountId": "YOUR_ACCOUNT_ID",
            "platformSpecificData": {"pageId": "111111111"}
        },
        {
            "platform": "facebook",
            "accountId": "YOUR_ACCOUNT_ID",
            "platformSpecificData": {"pageId": "222222222"}
        }
    ],
    publish_now=True
)
post = result.post
print(f"Posted to Facebook! {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 news from all our brands!",
    "platforms": [
      {
        "platform": "facebook",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
          "pageId": "111111111"
        }
      },
      {
        "platform": "facebook",
        "accountId": "YOUR_ACCOUNT_ID",
        "platformSpecificData": {
          "pageId": "222222222"
        }
      }
    ],
    "publishNow": true
  }'

You can also set a default page with POST /v1/accounts/{accountId}/facebook-page so you don't need to pass pageId on every request.

Media URL Requirements

URLs must be publicly accessible via HTTPS
No redirects, no authentication
Cloud storage sharing links (Google Drive, Dropbox) may not work -- use direct download URLs
WebP images are auto-converted to JPEG before upload

Analytics

Requires Analytics add-on

Available metrics via the Analytics API:

Metric	Available
Impressions	✅
Likes	✅
Comments	✅
Shares	✅
Clicks	✅
Views	✅

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

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

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

What You Can't Do

Post to personal profiles (Pages only)
Create Events
Post to Groups (deprecated by Facebook)
Go Live (requires the separate Facebook Live API)
Add interactive story stickers
Target specific audiences for organic posts

Common Errors

Error	Meaning	Fix
"Photos should be smaller than 4MB and saved as JPG or PNG."	Image exceeds actual size limit or unsupported format	Reduce to under 4 MB. Use JPEG or PNG.
"Missing or invalid image file"	Facebook couldn't process image -- corrupt, wrong format, or inaccessible URL	Verify URL in an incognito browser. Ensure JPEG/PNG under 4 MB.
"Unable to fetch video file from URL."	Facebook's servers couldn't download the video	Use a direct, publicly accessible URL. Avoid cloud storage sharing links.
"Facebook tokens expired. Please reconnect."	OAuth token expired	Reconnect the account. Facebook tokens have shorter lifespans. Subscribe to the `account.disconnected` webhook.
"Confirm your identity before you can publish as this Page."	Facebook security check triggered	Log into Facebook, go to the Page, and complete identity verification.
"Publishing failed due to max retries reached"	All 3 retry attempts failed	Usually temporary. Retry manually or wait and try again.

Inbox

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

Facebook has the most complete inbox support across DMs, comments, and reviews.

Direct Messages

Feature	Supported
List conversations	✅
Fetch messages	✅
Send text messages	✅
Send attachments	✅ (images, videos, audio, files)
Quick replies	✅ (up to 13, Meta quick_replies)
Buttons	✅ (up to 3, generic template)
Carousels	✅ (generic template, up to 10 elements)
Message tags	✅ (4 types)
Archive/unarchive	✅

Message tags: Use messagingType: "MESSAGE_TAG" with one of: CONFIRMED_EVENT_UPDATE, POST_PURCHASE_UPDATE, ACCOUNT_UPDATE, or HUMAN_AGENT to send messages outside the 24-hour messaging window.

Manage the persistent menu shown in Facebook Messenger conversations. Max 3 top-level items, max 5 nested items.

See Account Settings for the GET/PUT/DELETE /v1/accounts/{accountId}/messenger-menu endpoints.

Comments

Feature	Supported
List comments on posts	✅
Reply to comments	✅
Delete comments	✅
Like comments	✅
Hide/unhide comments	✅

Reviews (Pages)

Feature	Supported
List reviews	✅
Reply to reviews	✅

Connect Facebook Account - OAuth flow
Create Post - Post creation and scheduling
Upload Media - Image and video uploads
Analytics - Post performance metrics
Messages, Comments, and Reviews
Account Settings - Persistent menu configuration