When creating post (HTTP POST request to '/posts' URI) API responses with error model.post.is_valid.file_ids.app_error (Invalid file ids) when number of file IDs provided in request is more than five.
1. Auth in mattermost API to be able to interact with it.
2. Upload 6 or more test files to any channel (including direct channels) or get IDs of already uploaded 6 or more files, using the API call above.
3. Try to create a post with 6 or more files attached.
Observed: API responses with an not-obvious error 'Invalid file IDs' (model.post.is_valid.file_ids.app_error).
The server source code analysis shows this may be an unintentional behavoiur of server.
Error message "Uploads limited to 5 files maximum. Please use additional posts for more files."
Update to our API documentation that explicitly states the limitation on amount of files attached to a single post.
No testing required.