We have been testing the domain purchase flow in the Domain Mapping plugin, and our test users find it confusion. To buy a domain they are asked to log into WHMCS or create an account. But most of our clients / end users have no idea what WHMCS is. I strongly suggest allowing a variable where we can change that text and also add an explanation (e.g., "Your domain is being purchased from an external system. Please log in here to provide your domain registrant and payment information."...or something like that).