Please make a full backup of your site and check how it works with some default WordPress themes like TwentyTwenty or WooCommerce Storefront to understand if is it our theme issue or not.
Check the site on a device that has Google Pay or Apple Pay is connected – Eg your mobile device.
– This is solved and working.
You ignored my second question, when a user is logged in billing details still need to be entered, can this be auto filled if the user has this information already?
I am afraid Woocommerce does not provide the option by default, and you will need to search for a plugin, WoodMart theme as well as any other theme cannot have such an option.
If you have any questions please feel free to contact us.