We’ve all been there! Sometimes it’s just hard to make your client pay. Do what you can: keep reminding them. We don’t have payments integrated directly, but you can request a payment with a to-do field — by including your payment link (via PayPal or similar).
Pro tip. For the best results, tie up your payment request in a larger form with other fields. It will be obvious that you aren’t moving ahead in the project until the payment is made.