Overwrite Receipt.ss and DeliverySlip.ss in templates. on 404 after i.e. Mollie returns "paid" and order not found check if Emails can be sent without error

Debug Hint: set Order to paid in Database and call /OrderReceipt/StreamDeliverySlip/$OrderID and /OrderReceipt/StreamReceipt/$OrderID to test for errors

You may also need to apply the silvershop.patch for Address Fields to correctly display in default templates just add/require "cweagans/composer-patches" -> composer update -> add
"patches": { "silvershop/core": { "Made Address Fields not in composite field": "silvershop.patch" } }, to your "extra" in composer.json and update again (first one needed for composer-patches to install second needed for the patch to be applied)