That was normal in Texas ~15-20yrs ago. But in the intervening time, I've seen that become less common. I've run into places that won't let you pay after and will instead just ask you to prepay (full transaction) and come back in to get the difference refunded.

But I've also ran into plenty of places that if you hit "pay inside" on the pump will simply just turn the pump on, or will call you via the pump intercom (is that common everywhere?) and tell you they're turning the pump on for a max of XX gallons and to prepay or use the card at the pump if that's not enough.