The POS supports all three types of promo code you can create in the portal. That is
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These can be single use or reusable, we don’t differentiate the functionality. Although obviously a single-use promo code can only be used once (after the order is placed).
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Promos can be applied to an order through the actions menu in the top right of the POS
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Creating promo codes is not possible from the POS, if you’re looking to create a promo code, check out Create a promo code
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Click the actions menu

Select add promo code

Input the code your customer has given you. This will perform a check to see if it is valid

If the code exists, it will be applied to the order