When you get your License Key email, enter the information into the Registration dialog. IDImposer requires that all of the fields are filled with the exact contents of the email. Otherwise licensing will fail.
You should receive the License Key email with 10 or 15 minutes of when you purchase the License Key at PayPal. If it has been an hour and still nothing, check your spam mailbox, then contact us, at: firstname.lastname@example.org.