Domain for function

Hi. I am a bit lost using function, especially the part with the domain. I have a domain cookbooker-api.mesmoustaches.dev, and I can set my appwrite client using it, so I know it works. I would like to be able to call my function using short.cookbooker-api.mesmoustaches.dev, so I have set this domain short.cookbooker-api.mesmoustaches.dev in the domain tab of my function and set short.cookbooker-api IN CNAME cookbooker-api.mesmoustaches.dev. on my dns zone, but I have this error: Verification failed.

I am a mobile developer so all this stuff is very unclear to me, this is probably a very dumb issue, but I can't figure it out 😦