No, customer will be notified by WHMCS on your server when an invoice is generated. He the logins to his client area, clicks the PayPal Pay Invoice button, gets redirected to PayPal site and can use his CC again to pay.
So customer will need to login at every billing cycle to pay the generated invoice.
Thank you. Just what I needed to know. At least for now, that should be fine for me, as long as WHMCS will generate an invoice, that should be OK. As I get more success, I would look into CDGcommerce or something like that. Dave