Remote API and issues with "invalid client_id"

Hello,
I am creating a new client via remote api. I can see this client in isponfig.
But when I try to add a web domain via remote api, I have the issue that it doesn't work, the error is "SOAP Fault: Invalid client_id xxx".
I can add a webdomain manually to this cleint or I can add via remotge api a webdomain without client association an set it later in the frontend.
Just via remote api, I have this issue.
I am wondering how I can check what is wrong?
The ispconfig installation is running the current version.