Got tickets to the Gregory Alan Isakov at Red Rocks (with Colorado Symphony) - Can't go, asking for best advice for selling

Hey all. We got tickets way back in December, but sadly, we cannot go. We're sad to miss it, as his music means a lot to my wife and I. We tried reselling the tickets in AXS, at least just to make our money back, but haven't had any luck.

Any of you have tips on reselling tickets? We've never done this before.

Thanks in advance!