You’re right.
And what I’m trying to accomplish right now is, (if dynamicBase) not only set the clients position relative to the platforms position, but also to the platforms rotation. The only thing, what I can’t implement 100% right now, it sending relative accelerationInput data to the server, and (on the server) read them back to absolute values, based on the platforms rotation. Everything works until the server sent a small correction. I can see, the correction tries to fit the player into a wrong direction(acceleration) and it jitters(corrects) the player, until I stand still for one or two seconds. After that, I can walk around smoothly on the rotating platform. I guess, I need to edit the correction logic somewhere. But it’s really hard to find 
The wrong direction the player is facing, when he is jittering around due to the corrections sent from the server, is infact the inverseTransform of the direction in world space of the platform I’m standing on. So I just need to convert a direction vector (direction input or acceleration) somewhere from local to world space. But it’s really tricky. It’s the very last step, everything else works perfect.
edit: I think I found the last issue. The correction sends the velocity from the server, which should be wrong. I also changed the inputDirectionRotation to another position in code to a more direct one, which made the last issue more subtle and almost gone. I’ll check, if I can rotate the velocity or send relative velocity vectors. I hope this will fix it.