Post scheduled social content to Facebook, Instagram, and TikTok with Meta and Buffer

Description

Quick overview
This workflow runs every two minutes to fetch due social posts from your app, publishes them to Facebook Pages and Instagram (via the Meta Graph API) and to TikTok (via Buffer), and then reports per-platform posting results back to your app.

How it works
Runs every 2 minutes and calls your app’s /posts/due endpoint to retrieve posts scheduled for publishing.
For posts that include Facebook, it publishes either a photo or a video to the configured Facebook Page using the Meta Graph API.
For posts that include Instagram, it creates an Instagram media container for an image or a Reel via the Meta Graph API.
For Instagram Reels, it waits and polls the container status (up to 20 retries) until processing finishes or errors.
Once the Instagram container is ready, it publishes the media to Instagram using the Meta Graph API.
For posts that include TikTok and are videos, it sends a “share now” publish request to Buffer’s API and checks whether Buffer accepted the post.
After each platform attempt, it POSTs a POSTED or FAILED status (and any external ID or error details) back to your app at /posts/{id}/result.

Setup
Create an HTTP Header Auth credential for your app API and update the base URL and clientId query parameter used for https://your-app.com/api/n8n/posts/due.
Create a Meta Graph API access token credential (HTTP Query Auth) and replace YOUR_FB_PAGE_ID and YOUR_IG_ACCOUNT_ID with your Facebook Page ID and Instagram Business/Creator account ID.
Create a Buffer API credential (HTTP Header Auth) and replace YOUR_BUFFER_CHANNEL_ID with the Buffer channel ID for your TikTok account.
Ensure your app’s /posts/due response includes id, platforms, mediaType, mediaUrl, and caption, and that /posts/{id}/result accepts the workflow’s result payload.