I am one for always reading the T&Cs of a particular offer to make sure activating it is worth my while, however, even I have fallen foul of an omission on the latest American Express offer from ESSO of spend £30 and receive £5 cashback.
Now, I never fill up at ESSO as they are 7p/l dearer than my local garage near me, however, having done the maths, and realising I would be passing two ESSO garages on the way to a family visit, I decided to take advantage and still make about £3.60 net cashback.
What I didn’t do was click the link in the T&Cs to check Participating Locations. Had I done so, I would have noticed that there were NO local ESSO garages participating in this promotion. Neither of the two I passed (well, one of which I used) were included.
Hence, you guessed it, I have put exactly £30 in the tank. Paid by AmEx (instead of Chase) and waited for the cashback. And waited. And waited.
When it didn’t appear, I contacted their CS and, after passing security, and giving postcode of service station, was informed “Sorry, nothing we can do. But you still have until 2 Dec to try again!” 
Told them where to stick their card and their offers. Politely of course, as not the CS guy’s fault.
In fact, totally my oversight.
Just posted purely to warn others who may not check participating locations and fall foul too.
I hope to not be caught out again as many cards and companies make similar promotions.
For example, Costa, some promotions of which are not available at motorway services franchises 
I knew about them though 