@LaserPuzL: what got me on the right track is the comment at the very beginning from the Matter.MTRBaseDevice file. you can get there by using 'Jump to Definition' from the context menu on a related matter keyword in your source. it explains how to exactly decode the readAttribute response. this is the only place i have found that explains the encoding at all. just exactly reverse this using the correct datatypes described and it just works for invokeCommand.