What does it mean by ' receive 3 payments' in the FREE jot form, and why can I only add one payment type?

The three payments refer to the number of submissions that is about payments, such as purchases, subscriptions, donations, a free user can receive in a month.

On the other hand, in a form, this refers to the field you add in your form. You can only add one payment submission field. This means that you will need to select one out of the different payment fields like Paypal, Authorize.net, Stripe, Square, etc. 

If you have additional questions, please let us know.