Hi and welcome to the Community!
I have tried to reproduce the issue and the most likely explanation is that you unintentionally used another API key all the time and that’s why the API always returned the same error message.
- Using an Admin Key with all permissions works as expected.
- a) Using Admin key with restricted permissions to read Organization Administration fails as expected with the error message you posted above.
b) Using Admin key with restricted permissions to write Organization Administration works as expected
- Using an Admin key with Read ALL fails as expected with the error message you posted above.
Hope this helps!