@coflo yes, thats the problem. Polyend uses TRS type b . It’s not super rare, but to be fair, the A standard is more common. You shoud get an adapter TRS a to b, or a TRS b to 5 pin.
Here’s a web with a list of all the music gear and if uses a or b TRS. Indeed it’s a porblem of the music gear industry and not just a Polyend issue.
Hope it helps, been there myself.
EDIT: That’s why we sould read de manual. Been there myself too.
EDIT 2: here’s a thread about this issue and plenty of ideas:
https://backstage.polyend.com/t/trs-midi-cable-question/1317