How to send custom array of objects with post body? There is data classes PlaylistInsertOperation, TrackId and function insertTracks via Retrofit Interface. data class PlaylistInsertOperation( val tracks: List, ) data class TrackId( val id: String, val albumId: String ) @FormUrlEncoded @POST("/patch") suspend fun insertTracks( @Field("diff") diff: List ): PlaylistResponse When I send request, field diff equals the next string diff=PlaylistInsertOperation(tracks=[TrackId(id=39117009, albumId=5034819), TrackId(id=89341636,...