Each council in Wales decides independently whether to adopt the visitor levy and when. The Welsh Revenue Authority publishes a list of councils that charge the levy. If your council has not adopted it, you still must register your accommodation if you take bookings for stays of 31 nights or less, but you do not need to collect any levy.
Check council visitor levy adoption status (opens in a new tab)
Welsh Revenue Authority page showing which councils charge the visitor levy and from when.