Further investigation shows that Square Payment is somehow inserting itself into the OPC proccess. We were getting
Code:
paymentform:1 Uncaught Error: SqPaymentForm element with id `square_cc-number` not found. Has the DOM finished loading?
See: https://docs.connect.squareup.com/articles/adding-payment-form/#generatingpaymentform
    at s.buildIframeController (paymentform:1)
    at s.buildIframeControllers (paymentform:1)
    at s.build (paymentform:1)
    at s.build (paymentform:1)
s.buildIframeController @ paymentform:1
s.buildIframeControllers @ paymentform:1
s.build @ paymentform:1
s.build @ paymentform:1
And, we still got the error without OPC using PayPal and the standard, three-page checkout.
PayPal brings the customer back to OPC and Square is looking for the cc number.
When PayPal brings the customer back to Step 2 of 3 in the standard checkout, the Square error is also there BUT, it disappears when the customer goes to Step 3 of 3. Once on Step 3 of 3, PayPal will confirm even with Square turned on as the error disappears between steps 2 and 3.


The system goes through all steps including registering the New Customer, emailing info, order shows up, etc.


Again, ALL failed testing is done as never before customer, using PayPal from Split-Page Login.


Conversely, when a logged-in user orders an item and clicks on Checkout (OPC ON - Square ON), the OPC is shown with the options for a CC or PayPal Express. Choosing PayPal Express and clicking Confirm takes the logged-in user to PayPal and completes the order on return. It does not return to OPC to give the user the option to confirm but, goes immediately to completion.


Synopsis:


We were wondering why some PayPal orders were coming in and we were getting emails that PayPal would not allow others to check out. Current trials result in:


1. Customer NOT logged in and NOT a previous customer with both Square and OPC enabled
* Places item in cart
* Selects Check Out
* Arrives a split-login
* Selects PayPal Express
* Browser opens PayPal
* Customer selects method of payment and pays
* Browser returns to site with "uncaught Error" from Square
* Customer is unable to complete the transaction as the Confirm Order Button does nothing

2. Returning Customer Or Newly Registered Customer, logged in with both Square and OPC enabled.
* Places item in cart
* Selects Check Out
* Arrives at OPC with options for Square, PayPal, or Money Order
* Selects PayPal Express
* Browser opens PayPal
* Customer selects method of payment and pays
* Browser returns to site and completes the transaction without requiring any further action from the Customer


We are still not certain whether Square or OPC is the culprit but, one of them is "sticking it's nose in where it doesn't belong."