Activating the WolframKernel for Python

I would like to activate the WolframKernel to use Mathematica in Python. Although it worked the first time, later the error

Failed to communicate with kernel: C:Program FilesWolfram ResearchMathematica12.1WolframKernel.exe.

appeared. When I open the WolframKernel in this folder, it asks for activation. Maybe this is the reason for the error.
Unfortunately, I don’t know, what to enter in the dialog

Mathematica 12.1.1 Kernel for Microsoft Windows (64-bit)
Copyright 1988-2020 Wolfram Research, Inc.

Mathematica 12.1.1 Kernel cannot find a valid password.

For automatic Web Activation enter your activation key
(enter return to skip Web Activation): 

I tried the activation keys that I got in the Wolfram User Account, but they don’t work.

Best regards