Is there a trick to paying cash while using McDonald's app?

A long time McDonald’s casher who shall remain anonymous told me today that there’s a trick to paying cash while using the app. She indicated that once the debit or credit card used to set up the app expires, if you don’t update it, the cashier will just ask you to pay cash since the card can’t be charged.

Can McDonald's cashiers help customers pay cash?

The manager of my local McDonald’s confirmed that cashiers can help customers pay cash for an order they placed through the app. However, in practice, I have found that cashiers often don’t know they can do this. When I spoke to the manager, he said he would speak with his cashiers to make sure they understand how it works.

Do rewards/discounts apply if I order through the app?

It’s also unclear if rewards/discounts are applied if you order through the app but request paying in cash. It may be that the entire order is redone at the store as if you weren’t using the app, and that rewards/discounts don’t apply.