So I have had a new eCommerce site running for a few months now and we have had a few offline payment orders come through, so it has been tested and working nicely. I have watched the users run the process via hotjar to see if there was any confusion going through the offline payment process and no obvious friction points were found.
So you can check out the solution here: https://www.commercialdehydrators.ca/
If you add a product to cart and then click on offline payment option it will take you to the offline checkout form showing your cart items and totals on page. So it is essentially another checkout page and can also validate form info and once submitted it take the user to a confirmation page with bank wire details with the order amount.
Once the user has made the offline order they will be entered into a specific workflow in the CRM that sends a Xero invoice.