You send a request to a contact to use your portal app. What should they enter when signing up to the portal to link their user to their contact record?

While an email address is used for authentication, it does not automatically link to an existing contact record during an invitation process unless specifically configured for identity matching, which is not the primary linking method.

A full name is part of a user's profile information but is not a unique identifier used to link a new portal user to an existing contact record via an invitation.

Power Apps portals utilize invitation codes to securely link a new user's sign-up to an existing contact record. The user receives this unique code and enters it during registration to establish the association.

A web role defines permissions for a user within the portal after they are linked to a contact, but it is not a code used for the initial signup and linking process.