Sling back iridescent sandals

Super beautiful iridescent sling back sandals. I want to keep them but they don’t fit, never worn brand new condition. I’m normally a 9 and these are tight on me even tho they are size 9. I am going to post them as a size 8 because of the fit. I never had sling backs so I wasn’t aware to size up. Lining: 100% Polyurethane, Sole: 100% Rubber, Upper: 100% Polyurethane.