Rust Dedicated Server Admin Problems

Can anybody help me?
Every time I try to use the owner ID admin @ command it says that this isn’t a steam 64, but I know it is.
It’s a 17 digit code, but I can’t admin no matter how hard I try.

Try you code…

Use your number instead of xxxxx

I am looking to be an Admin on a Facepunch Rust sever, any suggestions?