Are tips mandatory in Oxford? If so, people wont accept me to tip by card so what should i do when i dont have irl cash?

In my country they usually come included as a sugestion in the bill and you pay by card but people dont get mad if you dont tip them, specially if it is like an uber or something. In US is really rude not to tip and i am not sure about oxford. Just tried to tip a lady by card and she was super confused