panning reverb on mono track in sends

Im trying to pan a reverb (REVelation) in Sends, but the panning button doesn´t show. It´s a mono vocal track. In Sends it´s routed to a FX-track with REVelation on it. But the panning button in Sends isn´t there,
It works on the stereo tracks, but not on the mono-tracks. Where the panning-button should be its just grey. If i right click, it´s says i can bypass and copy and send, but nothing happens.
What am i doing wrong?

Insert the reverb on a stereo track.

Im blushing. Thanks.