It should have no issue at all to align German wide but they never did it.
The Munich MVG for example is doing an experiment were you can pay by an app from some us company were you just start and stop your journey with a button and the app gives you the best price.
They could have instead just created some German wide software company sponsored by all the local public transport agencies and just do it themselves.
It's ridiculousl that modern problems are often not technical problems:-(