You could only retrieve the campaigns using client accounts that's why you won't be able to retrieve your campaigns using a manager account (if you have set your clientCustomerId as your manager account in the property file). The
AuthenticationError.CUSTOMER_NOT_FOUND you encountered normally occurs when you are trying to access an account that was just created with
ManagedCustomerService before the account is established in the backend. This being said, could you try again to make a request using your test client account?
If the issue persist, could you provide the complete SOAP request and response logs so I could further investigate the issue? Please reply via Reply privately to author.