Generally speaking, contacts must already be created in Pylon for them to login to the customer portal.

You can configure the auto creation settings on the Customer Portal settings page in order for contacts to be auto created on login with your default role if they do not exist.

Contacts are associated with an account based on the domain of the contact trying to login. For example, if you have an account with domain example.com and the contact attempting to login has email bob@example.com, they will get auto created into the corresponding account. If there is no corresponding account, they will not be able to login.