Hi Mohammed Nazeel
Most offers require you to meet certain criteria before the credit will show up in your account, and they’re typically for new advertisers with new accounts. Be sure to check the terms that came with your promotional code for details about your offer.
For example, we might have an introductory offer like “Spend $25, get $50.” In order to get the $50 credit, you’ll have to enter the promo code within 14 days of creating your account and then get at least $25 worth of clicks in your account after entering the code. After spending $25, you’ll then see the $50 credit appear in your account within 5 days.
See more: https://support.google.com/google-ads/answer/6388096?hl=en