DT Billing is intended to be used with the standard paypal account. You do not need to setup any return URL... DT Billing handles all of that. If you are setting up other things on the paypal side, you are very likely messing up the intended process. Let it do its job without interference and you should be okay.
Well, it was not intended for PayPal Pro use and never tested with it. It is designed to use a standard paypal account. As we haven\'t check into the integration of the Pro account, I can\'t say whether or not the component could work with PP Pro or not. All I can say is that we\'ve never tried it ourselves and that we have never promoted our components are supporting PayPal Pro.