Legal tender only applies to debts, so all creditors have to accept it to settle debts, but private businesses don’t have to accept it in exchange for goods/services. They are free to accept payment however. It’s the same in the US; lots of places only accept credit cards.
Discussion
Except, if they've already given you the goods -which is the typical workflow in a shop, restaurant etc- then they're legally required to accept your cash, as it's now a settlement for a debt.
[They you never serve you again, but that's a different question 😉]