Hello @philipp.schmieder,
I believe this post here might be of help for you.
The error message you are getting:
Warning: Cannot get compatible board name.
Seems to be related to the board configuration you are using to generate the OTA payload.
Please give that blogpost a read and let us know if helps.
Otherwise, we will continue helping you find the cause of the problem.
best regards,
Andrew
Embedded Software Engineer at ProventusNova