If an end customer requests a receipt, it is the merchant who is responsible for providing it.
In some cases, the end customer can contact the payment method to obtain a payment confirmation. Combined with your delivery confirmation, this is often sufficient as an approved receipt.
However, if the end customer requires an approved VAT receipt, this must be issued by you as the merchant, since the purchase was made from you.
A good approach is to generate and send a receipt with every order, for example on your confirmation page.