All discount codes need to be submitted during your checkout. If the discount code does not work or it is not accepted we kindly invite you to check the expiration date or double check if you are entering it correctly. Also, take into consideration that as per our promotional terms and conditions all discount codes are deactivated during special sales on our website.
https://rounderbum.com/pages/promotional-terms-and-conditions
Once products are at regular price discount codes are reactivated and ready to be applied. After taking the aforementioned point into consideration and you still have problems please reach out to our Customer Support Team.