Every few weeks I get an email from Uber Eats with a generous-looking promotional code, to the tune of 25% off. If I line up an order on the website and enter the promotional code, no discount appears on the order. If I refresh the page and re-enter the code, it tells me That code has already been used.
This has happened to me 3 times now, if I recall correctly.
It's not as if this can be blamed on my using a peculiar browser. Last time this happened I was using Edge, with no plugins or funky configuration changes.