I think the problem in alot of cases may be that you have to click pay by card depending on what version of Tesco’s software it’s on,
You used to be able to tap a contactless card when it was on the payment screen where it asks you how you want to pay, cash/card/voucher and it went through.
But since they started with NFC clubcards on that screen it only accepts clubcards unless you click on cards.
If you try contactless at that stage your phone will get a tick on the screen, it will say processing and then it will decline.
I have 2 local Tesco’s one seems to have an update that now you can do contactless on the cash/card/voucher screen and it goes through but the other Tesco still doesn’t let, so hopefully they’re rolling out new software.