add_to_collection
Add a post that is on the platform to a collection (YouTube playlist, or save a Pin to another Pinterest board). position 0 puts it first; omitted puts it last. For a post still 'scheduled', set metadata.playlistIds instead. Needs the manage permission. Also available as the MCP tool add_to_collection.
POST
https://mixetape.com/api/v1/tools/add_to_collection