Duplicating a car key is a very specific type of key cutting. When an auto locksmith duplicates a key there must be a working key present at the time of the key cutting. Duplicating a car key uses a key duplicator. This is different from something like a code cutter, which can be programmed to cut a key based on the numerical representation of its physical appearance. A key duplicate may have some amount of automation, but it needs a key to examine in order to cut a copy of that key. When there is no extra key present to be read by the machine, the duplication process cannot be used. This is not to say that the key cannot be copied. It will just need to undergo a different process in order to create a new spare.
A key duplicator takes the knowledge of an experienced auto locksmith in order for it to work correctly. The machine needs to be oriented properly between its blade and the key reader. The keys must also be set up correctly in the key duplicator. Between these different calibrations, a lot could go wrong for a novice. Because this process uses a bit of artistry, it is not an exact science. This will not stop your key from working correctly unless you are using a copy of a copy to make your duplicate. The farther removed a particular copy is from the original, the greater the chances of it not working in the car. Always give the auto locksmith the original key (or the closest to it that you have) when you are requesting car key duplication.