AbleCommerce Shopping Cart Software

Is there a way to add an optional PO Number field to the various payment methods?
Some of our customers want to pay with a CC but include a PO Number for reference.
Gold R9

You will have to do some custom coding. Probably you will need to add a texbox to credit card payment form and then save its value into a order note for reference. Although same can be accomplished by manually adding an order note from receipt page after order placement.

If you have enabled customers to add order notes on their receipt page you can prompt them to use that for PO numbers.
On ../Checkout/ShipMethod.aspx page I edited the ShipMessageLabel (around line 105) to read... It looks like the attached image and works like a charm!

Thanks for the suggestions. I think I'm going to try to add this as a custom field. I'll update the post if/when it works.