Validating Invitation Codes
The invitation code for each of your users is simply a SHA1 hex digest of your secret invitation decoder key followed by their e-mail address. Therefore, to validate the invitation code you will simply need to calculate what you expect the invitation code to be for a given email address and then compare the result to what the user has provided.
Basically, this means that validating an invitation code is nothing more than a bit of math and string comparison, so there's no need to use our API.
If you have enabled the use of short invitation codes in Prefinery (which are enabled by default), you only need to validate the first 10 characters of the calculated invitation code.
Your project's secret invitation decoder key, used for validating a user's invitation code, can be found within your account on the Beta Management Settings page available via the Settings -> Project Settings menu in the upper-right corner of the page.