Creates a submission for a smartdoc. If the smartdoc doesn't contain any fields, or if wrong party IDs are given, it cannot be submitted and the endpoint will return a 422 - unprocessable content error. The parameter contact_id is deprecated. Use party_signer_ids instead. The parameter party_signer_ids is an object mapping party ID to contact ID: keys are party IDs and values are contact IDs. Give as many key-value pairs as there are parties in the smartdoc.