In Spain you are allowed to drive the 3-Wheeler with a regular car license. That's according to the Spanish regulations, and my bet is that they are respected across Europe. Why would a German Police officer stop you looking for your A motorcycle license? I can only think of it if you have a non EU plate, such as the UK one. Can you confirm this applies only to UK drivers? Because, I insist, with a EU type B license you can drive the 3-Wheeler without being bothered.
I've done a little google research and it does look as if the EU licencing situation is changing with some countries appearing to be introducing the EU directive conditions.
For Spain it is clear, as Marmota says, that currently a B licence is fine.
For Germany it appears they have recently changed the requirement from B to A as shown in the first section of
https://www.tuev-nord.de/en/services/driving-licence-and-vehicle/motorbike-driving-licence/ This it might explain why we were stopped at the border.
France is a bit confusing with the gist seeming to be that you need A but can use B in certain circumstances which might be a reference to grandfather rights if you passed your driving test before or until they change.
Italy and Switzerland seem to still be B
All of this is my understanding based on limited research and not definitive nor is it advice. As always it's your own responsibility to make sure you are properly licenced to drive your three wheeler!!
