Yes, permits are required for retailers. You also have to stock certain items in each dept. to be eligible. Something like a 7-11 doesn’t qualify because they don’t carry enough foodstuffs. The retailer can also refuse to play. I get inspected by the state once per year to be sure I carry all the qualifying items.
You cannot buy alcohol, tobacco, or dry goods on food stamps. Nor prepared food from the deli.
Just about all the convenience stores here, including 7-11, accept the Washington State EBT cards now. They have signs up stating that in their windows. Eligible items are charged separately from non-eligible items electronically; no need to sort them out physically (an earlier comment was unclear on this).