Thanks for contacting us regarding Pie-Register. Well, all you need to do is to make sure that WP-Login is override by PR generated login page (You will need to block wp-login from PR General Settings page) and Paypal is Enabled and Configured correctly on PR. User will have to pay for the Registration and without payment their account will not activate. All those users are listed on Unverified Users page. Where you can resend payment link to them.
I hope it helps. Please feel free to post if you have further questions.