As of April 12th, you must go to Progress SupportLink to create new support cases or to access existing cases. Please, bookmark the SupportLink URL and use the new portal to contact the support team.
If the user logging in is not present in User collection then you will get "Invalid Credentials" error. Can you please check this link and let me know if this is what you are looking for?
Also, for a better understanding of Kinvey Business Logic, please review the following links: