Answer
A normal retailer voucher code does not require you to pay a separate fee to enter it at checkout. Coupon websites can earn affiliate commission when shoppers follow merchant links, but that is separate from the retailer price.
Always review the final retailer checkout total, delivery charges and subscription conditions before paying.
What to check before checkout
Read the retailer’s current promotion terms, confirm that the code applies to the items in your basket, and make sure the expected saving appears before you pay.