You can exclude the purchase of vouchers via certain payment methods as follows:
Go to Products → Categories, select your online shop on the left in the list, and click Add to create a new category Vouchers. Then open the Products tab and assign all voucher products to this category.
Open Settings → Rule Builder (Riskmanagement) and select the payment method for which you want to block voucher purchases. In the section Block payment method IF, select the option Product from category and enter the ID of the voucher category in the field next to it. You can find the ID in the Categories window (see screenshot above).
After saving, vouchers can no longer be purchased using this payment method.
Important: Shopware's risk management only takes into account the payment methods selectable at checkout, not the default payment methods preset in customer accounts. Therefore, customers who have set the excluded payment method as their default payment method in their customer account can still use it.