Problem Audi A3, The problem with the keys


Hi. I'm selling an Audi A3 from '99. I have 3 keys, one key, one normal and the last plastic. The key has suffered something in its life and it barely holds. So, I say, it doesn't make contact all the time , and once every few days, the car doesn't start with the first key. Ok. What I said, until I get money, I use the normal key. Today I noticed that that key is not from my mother's car. So it was a bit crazy. The key is only slightly different from the key and I can turn on the ignition but it does not recognize my code. Is there any possibility to program the second key?