Most probably the issue is with Speedway and not with
Giftcards.com. I have found that many of these gas apps don't work well a lot of times (the exception being the ExxonMobil app, which I have never had an issue with -but have only used them a few times.)
A few years ago there was an Amex offer for Conoco / Philllips 76 - out of 6 gas stations, only once was I able to get their app to work.
And BP, don't get me started with their app. In NJ, it is state law that you are not allowed to pump your own gas. Well, in the BP app, once you authorize the pump, you must start pumping within 45 seconds or it times out. So I pull into the station and start authorizing the pump and the attendant didn't want to wait so he goes to another customer. Of course, by the time he gets back it was more than 45 seconds, so now I have to authorize the app again. So again, he doesn't wait and goes to another customer, and again, by the time he gets back the app times out. After doing this 3 times, I finally said to the guy, it only gives you 45 seconds and you keep walking away for more than 45 seconds - just wait here until I get it authorized. He gave me a dirty look but waited. After that, I never went back to a BP station.
Also, some of these gas companies have all sorts of fine print that you don't realize until afterwards. For example, Shell only allows e-gift cards and not physical gift cards to be loaded into their app (presumably because e-gift cards are only sold directly from Shell and can't be bought at a discount).
For this reason, I stay away from gas gift cards. Instead, I use my sisters Costco account to buy Costco Shop cards and use those to buy gas at Costco. If you have any family member or friend who has Costco membership, you can use their account to buy Costco Shop cards and have it shipped directly to your house.
(The other gift cards I stay away from are airline gift cards since most of them will only allow you to pay for the flight itself and nothing else with the gift card, which is a bunch of garbage. Also, I would much rather pay for flights with points, because if you cancel the flight, you just get your points back which never expire on most airlines as opposed to if you pay with cash or gift cards you get a voucher which has expiration dates. The exception is American Airlines, where points expire if you don't have activity in 24 months.)