Hi there, Jeff.

I'm here to assist you with your concern about using Custom Fields today. The Custom Fields feature can be used for any information you want to add that will show on an invoice you send to your customer. You can use and rename the Custom Field into Payment Method so your customer can see the applicable payment method.

You can add another Custom Field for that Payment Method or use the same Custom Field you already set up. 

Here's how:

1. Go to the Gear icon and select Custom fields.
2. Click the Add Custom field button.
3. Enter Payment Method as the name.
4. Enable the All Sales forms checkbox and the Print on form.
5. Click Save.

Moreover, you can also consider creating recurring invoice transactions to save time and use the same transaction with regularly scheduled payments.

If you have additional concerns or questions about using custom fields as a customer payment method, please feel free to reply below. I'm always here to help.