Hello @brett-haralson that tutorial if for creating a payment with Wix Pay. Not to add a new payment gateway.
I’m in the same position. We need to add our own service payment provider to Wix and I don’t think it’s possible.
@OP It’s there are solutions in place for payment providers to integrate Wix “easily”. You could ask Mobile Mobile to contact Wix support to integrate their solution into Wix