The most common reason for a Donations app page to be missing the billing information section (such as credit card fields, address fields, etc) is due to a mismatch between the domain used to load the page and the configuration of the Soapbox Engage payment gateway setup that may use a different domain.
For instance, if you're visiting the web page https://example.secure.nonprofitsoapbox.com/donate, and your Soapbox Engage payment gateway integration is using https://donate.example.org as its root domain, that would likely cause this issue.
A fix for this would be to open a support ticket with our team to make sure the appropriate domain is being used for your payment gateway connection.