Answer
No. A voucher code normally reduces an eligible checkout price immediately, while cashback is usually tracked separately and paid later if the transaction meets the provider’s conditions.
Some cashback providers restrict use of codes that are not listed by them. Check both sets of terms before combining promotions.
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.