One of your keys is currently untradable, probably because you bought it recently, you will have to wait a little, steam says it will be tradable after "Tuesday, September 20, 2022 (7:00:00) GMT"
The keys used as currency in trading are the "Mann Co. supply crate key"s, the "Summer 2022 Cosmetic Key" is a different one, but can be exchanged for regular keys on the "items" tab