I travel 60-70 nights a year. This was probably the most unorganized and unhelpful hotel I've ever stayed at.
As others have pointed out- they have no front desk, so they send two links- one is for checking in online, the second is to pay the city taxes.
The first link they sent was obviously broken, and they didn't respond to a request for a correct link for almost 3 weeks. I finally had to call FIVE times the day before check-in- their Whatsapp wasn't working, they weren't receiving emails, they weren't receiving text messages.
They didn't respond to hotel.com messages either. Finally hotels.com called their number and got them to send an actual email with the correct links after I told them I would cancel the reservation if it wasn't received (remember, no way to enter the hotel!).
Upon arrival- their advertised air conditioning didn't work, and the thermostat was dead. I called their support line- the lady on the phone, who couldn't have been more unhelpful, demanded proof that the thermostat was dead, and asked for a video. So I sent a video- she was supposed to call me back, and did not.
At that point I wrote it off. Do NOT stay here under any circumstances if you wish to actually enjoy your stay in Venice.