My client is facing an issue with checkout related Shop Pay express checkout that I can wrap my head around especially since the checkout experience is locked down.
***This online store only offers in store pick up
When a customer goes to checkout and selects Shop Pay the delivery method of "local pick up" is NOT propagated over, so the shop page remains frozen as it try's to calculate a shipping price for an item that does not support shipping. This is preventing customers from checking out.
However I have noticed that if customer selects "continue to payment" (aka NOT selected Express shop pay button) .... and then goes back ( clicks "return to information") .... and then clicks express checkout shop pay button, only then does shop pay properly capture the correct delivery method. So something about moving to payment page and then back is adding something useful to the session that then allows shop pay to behave as expected ..... but this is not a normal flow for customers, I was only able to find this through many trails of trying to understand. the bug.
I have included some images to help visualize this issue (images include: check out page where Express Shop Pay button is clicked. Image of frozen shop pay screen due to trying to calculate shipping. And then another image of a proper shop pay screen with "local pick up" captured)