We have an requirement where the user's shipping/billing information is maintained in custom table and the respective registered user in Magento store need to complete the checkout process(selection of billing/shipping address from custom table).
Currently we are able to display and select shipping information from custom table by overriding checkout knockout js component, but each time on selection of shipping address it uses following api call "V1/carts/mine/estimate-shipping-methods-by-address-id", which uses estimateByAddressId method and uses users addressid.
Since we are not maintaining the user addresbook it throws error(no such entity with addressid exist).
Request forum members to suggest optimal solution to achieve this requirement.
I don't why you need such a big change.
but you can pass your ID when somebody selects that address, on the server side that API implementation method you need to get all info from your table and pass necessary into to Magento quote.
Hope it will help you.