Need help connecting n8n → Buffer (GraphQL API) for LinkedIn posting

Hey everyone,

I’m building an automation to publish LinkedIn posts through Buffer using n8n, but I’m stuck on the API mutation step.

Stack I'm using

n8n (self-hosted via Docker)
HTTP Request node
Buffer GraphQL API
Bearer API token
JSON request body

What works so far• API authentication works• I can run GraphQL queries successfully• I retrieved my organization ID and channel ID• Queries like fetching account / organizations / channels return data correctly

Where it breaksWhen I try to run the createPost mutation to create a LinkedIn post, I consistently get a 400 error.

I suspect the issue is related to the CreatePostInput schema requirements (fields like shareModel, schedulingType, text, etc.) or how n8n formats the JSON request.

GoalAutomatically create or schedule LinkedIn posts in Buffer from an n8n workflow.

If anyone has successfully done n8n → Buffer API → LinkedIn posting, I’d really appreciate seeing: