While filling out a form in NetCommunity, the URL changes from the NetCommunity URL to a URL that starts with payments.blackbaud.com. You want to know why the URL is changing.
Pages that include a secure part, Event Registration Form (non classic) and Payment 2.0, utilize the Blackbaud Secure Payment Server. These pages navigate to payments.blackbaud.com when the billing information is collected. This is a normal process.