Can't add FX to mons

[mattlawtonbass]

I’m struggling to add FX to a mon mix. The FX can be added to main LR mix, no problem. When I select a mon mix and raise the fx return it has no effect. Can somebody please troubleshoot this with me? Thanks

[SQuser]

Are you sure that your FX Returns in the Mix Sends are also switched On?
(See picture and also page 42 of the manual.)