If you are looking to only offer online payments as an option on a registration form, but still provide the ability to pay offline (via transfer, cash, etc) to a select few users, you can share an offline payment URL link with them.
By sharing this link, it allows the user to complete the registration form without paying with a credit card.
To share the Offline Payment URL:
Go to the Registrations tab
Find the form you are looking to share. In the Actions column, click More > Get Share Link
3. Share the Offline Payment URL with the user