Aux send from mono track to stereo bus?

I would like to create an aux send from two mono tracks to a stereo effect bus, but the option to add Aux send is greyed out. If I set up a mono bus I can add an Aux send to that one.

Is this not possible from mono to stereo bus? I’d like to avoid having to create seperate mono busses for each track as I have effect automation on the bus.

Also tried with an external send and routing that in the patchbay, but no signal arrived at the stereo bus.
Thanks in advance!

Ok I think I did something wrong, I created all tracks and busses again and now it works…