Guusto gifts can be redeemed with thousands of merchants, so it's likely many merchant staff will have never heard of Guusto if you just show them the website or app.
However, when you open your gift, select a merchant, and click the "view gift code" button, the system will open a webpage with a merchant gift card (exactly like one bought off the merchant's website, see sample image below). They will recognize this and redeem it like any regular gift card.
Click here for detailed instructions on how to redeem your Guusto gift.
The Guusto system integrates directly with the merchant's digital gift card processor. If you have clicked "view gift code" and you see the image of the gift card that includes a bar code or 16 digit number, and the merchant is still having problems redeeming, it's likely that there is an issue with the digital gift card processor or their payment terminal.
In this case, they offer phone support. Each merchant support phone number is different, and is located at the bottom of the gift card.