Quote Originally Posted by lat9 View Post
@dbltoe and @haredo, rather than replying with quote I thought I'd save the zen-cart site a little storage.

My initial hunch is that there's something that OPC needs to do to "convince" Square that the payment method is already determined and that it (and any other payment-module except for Express Checkout) can "bow out".
OK, I've had a chance to look into this a bit more. It turns out that there is also an issue with OPC and payeezyjszc during PayPal Express Checkout (i.e. like the customer can't complete their PP-ec purchase due to a jQuery issue).

The issue with OPC (and possibly the 3-page-checkout mode as well) is that all enabled payment methods are being loaded when the current order is being paid with PayPal-ec and some of those methods' javascript/jQuery scripts are getting confused since their payment-selections aren't rendered during "special checkout".

It might take me a couple of days, but I've at least got a direction to look!