Before you start, keep in mind that:
Promo code are case-sensitive, so make sure you enter the promo correctly.
Promo codes can be used only once,
Promo codes can be only for your store.
Login into the store and open Rush App. From there, go to the Billing tab and click on Redeem Promotion Code button.
Enter the name of the promo in the modal:
On success, you will see the promo code applied and similar messages to this:
And your promo code details will be visible in Redeem Promotional Code section.