New Shopify store just launched. When trying to pay with Google pay the message “Your payment couldn’t be processed because your order total has changed. Check your order total and try again.” is received. Payment with Paypal and ShopPay works fine.
I think the issue is that when Google Pay is selected the shipping address is not yet known and therefore the shipping cost is not known. When the delivery address, the one within the Google Pay profile, is selected then the shipping cost is added but Google Pay sees this as an increase in the order total and doesn’t like it.
But Paypal and ShopPay handle this ok.