file_id you got back from the upload response as the file_id path parameter.
The run is asynchronous — poll GET /v2/workflows/{workflow_id}/files/{collection_id}/results/ (using the collection id from the response below) for the output.
file_id is the file_id from the upload response — the individual file handle, not the file_collection_id. See Files and collections. For upload-and-process in one call, use Run Workflow instead.