Taxi Payments

You can use the app. There are several.

You'll have to first confirm the driver is equipped with a Tap and Pay system.

Cash is also fine
No tip.

Taxi drivers are infamous for refusing electronic payments, as their declared income is often unrealistically low and they do not want it to be traceable.

The only way to pay electronically for a taxi, regardless of whether the taxi driver likes it or not, is to use the app.
There are several one can use, depending on the city you are in.
In Florence, for example, it's AppTaxi, or TaxiMove (there are two main companies which use either), in Rome it's ItTaxi. The latter has an agreement with Uber, therefore you can access it via Uber app as well, albeit Uber adds at fee (I think around 3€).
FreeNow also works in most cities. By using the app, you can pay via the app, and not be pressured by the taxi driver to shell out hard cash.