Kensington lock doesn’t seem to fit, iMac

Hi, I own an iMac 21,5” from 2016 and wondering whether I can use a Kensington lock on it? The store I bought it in says it is a Kensington lock on the backside of the iMac, but the cable I own doesn’t seem to fit. It fits my two Lenovo laptops though. I have tried to apply some pressure, but the hole isn’t big enough in the curves. I have searched the web for some time and I can only find an article about a 27”, but it states the same as the store. Well, I hope some of you can guide me wether I should get a different cable?