Can we manually enter in a registration form with payment on JotForm directly?

Are you planning to prepopulate the form fields? It is possible to prepopulate the fields via the URL. I suggest you check the Field Prepopulator app.

If you want to do it manually, then please check this guide: https://www.jotform.com/help/71-Prepopulating-Fields-to-Your-JotForm-via-URL-Parameters.

Hope that helps. If I misunderstood your issue, please let us know. Also, please provide more details so that we can assist you properly. Thank you.