Very useful, but app payment doesnt really work

I use this app around Berlin and it very useful at calling taxis. More respond to this app than Uber (in Berlin Uber is taxis). The one problem is that most of the drivers do not take payment with the app, even if you specifically request one that does. They cant figure out how to process the payment or they dont want to and seem surprised that I expect it after including it when I made the request. One of the nice things about Uber is not having to worry about having enough cash. If this app could address that issue, it would be ideal.

MinnaB about taxi.eu