Every call fails with 403 AuthZ_2.0 "Your brand does not have access to this API endpoint."

I tried both the token and the oauth approach with just a simple whoami call (also tried other calls like retrieving a survey).
The URL shows me "az1" as data center id (https://{orgid}.az1.qualtrics.com/) which returns me with the error to use scj1 instead of az1. Irrespective of what I use, I end up getting:
"httpStatus":"403 - Forbidden","error":{"errorCode":"AuthZ_2.0","errorMessage":"Your brand does not have access to this API endpoint."
The call to https://az1.qualtrics.com/oauth2/token with clientId and secret returns me an access token. But neither works.
two samples:
curl -X GET -H 'X-API-TOKEN: {API_TOKEN}' -H 'Content-Type: application/json' 'https://sjc1.qualtrics.com/API/v3/whoami'
curl -X GET -H 'Authorization: Bearer {BEARER_TOKEN}' 'https://sjc1.qualtrics.com/API/v3/whoami'
Can any one advise what I am doing wrong or what is missing in my account?