Spare Key Transponder doesn't work

I brought my 2003 (03) Astra in for some body work and gave the garage my spare key. Now I never used the key before in my life (owned the car since 05) and used my original to drive to the garage. I got a call a few hours later saying my spare key doesn't work and that they had to push the car in the garage. Key doesn't work bc the transponder wasn't tuned in to my car's immobiliser.

Vauxhall dealer wants to charge £40 to tune it in. Does anyone know how a layperson such as myself can do it?

Thanks

You can pull the key apart and make sure the little transponder chip is in the key. If it is not there, it may be cheaper to buy a new key and have it chipped at the same time.

If it is there, then some local key cutting places can usually code the key for you if you have the original.