I’ve had this in Barcelona even when booking a hotel directly through its website. It was advertised up-front but unsure if there was any reason they couldn’t

I’ve had this in Barcelona even when booking a hotel directly through its website. It was advertised up-front but unsure if there was any reason they couldn’t roll it up into the fee. Maybe it is a separate city-issued POS? Or maybe a tax thing: if the hotel collected it, they’d have to charge VAT, but not if the booker pays it direct?