Before proceeding, please confirm which platform which platform your promo code is corresponded to. Promo codes are not valid interchangeably, with the exception of subscribed members.
iOS
Method 1:Within Grid Diary app, in the purchase interface, click on "Redeem Offer"
Method 2:Or click in the order: Me-> Help-> Redeem Offer
Enter your promo code and follow the in-app guidance
Android
Enter the purchase interface, click on "Redeem Offer"
Enter your promo code
When the offered price appears, proceed to purchase.