redeem coupon on active campaign
Is your cupon for new advertiser only?
Promotional codes are typically limited to one per customer, and are often for new advertisers only.
Welcome to adwords community,
Promotional codes are usually only meant for new advertisers, providing an easy way to get started with the AdWords program. Therefore, these codes can only be redeemed up to 14 days after the creation of an AdWords account. If you created your AdWords account more than 14 days ago, you won't be able to redeem the code.
Note that Google won't accept or replace expired vouchers.
Re: redeem coupon on active campaign
As discussed earlier you can follow this steps before renewal of promotion coupon on the account. If you are satisfying these conditions then redeem the coupon on the account.
Condition 1 - Account should not be older than 14 days.
Condition 2 - You should not have redeemed any coupon in this account earlier.
If you fulfill these conditions then redeem them coupon, you will get $300 updated in your billing summary once you spent $100.