Only 2 eurocents for 2 people vaporetto (one day) with 'tap to pay'

We just went to Venice for 3 nights and took a shared taxi (booked beforehand) from the airport that dropped us of our hotel, which was 78 euros. The one from the hotel to the airport was 170 euros.

BUT we also took the public boats a few times and were astonished by the low cost. We did it 2 days for 2 persons and it was only 2 cents, so we payed a total of 4 cents for public transport.

I checked my card 2 days later and nothing extra has been charged.

Sp please don't be worried about the pay for public transport, just use the 'tap to pay' stations.