Automatic email address creation upon purchase with web based access

I have a product which, when purchased online, automatically creates a unique email address and also user name and password to access their personal mailbox. This was working fine and now is creating the email address, but the user name and password which is being created is NOT producing a working user name and password, so the customer can't access their mailbox to check emails.

AWS is used for the email creation and also directadmin.