In the Magento 2.x core checkout, as well as all the 3rd party One Step / Single Page checkout modules, magento makes the user click an "update" button to save the billing address before checking out. This is when the billing and shipping are different.
If you user does not click it, the card is denied because it's using the wrong address.
The is the source of the most frustration and anger with all my clients. They all get 100s of customer calls because they miss this button or don't understand it.
PLEASE HELP ME KILL THE UPDATE BUTTON.
There should be no need for it. It should simply use this address when Checkout is clicked.
Any pointers how I can get rid of it in and save the billing address on Checkout click, in a way that it doesn't come back on the next Magento update.
