This is an error with the customer credentials in ConnectWise Manage. It is likely that the user has provided the incorrect Manage Member password when providing credentials, or that the Member is using LDAP, i.e. Windows Authentication, in Manage, which is not supported by the ConnectWise API.
Another possibility is that the user may not have Admin or GL Interface rights. To resolve, go to the Member setup and verify the ROLE ID associated with that user has rights to access the GL Interface in Security Roles.
If the user does have credentials to access those areas, then please reach out to ConnectWise directly.