The silver GM Keys will have a letter stamped on/into the key from A - thru - E and they are all the same key with different lengths.
Could be a simple as the wrong length key vs the barrel. Same is even true for the plastic head keys.

If you have a 4 digit code on a genuine barrel I can factory punch cut a genuine GM key for your barrel. If it is a Chinese aftermartket replacement product then I can't help.