Hi @JPFiber
Not sure about the official way of doing it but something like the below can work?
Try getting the value for your zip code through Response token and for testing purpose use that zip code as part of the XT audience. Haven't gone granular to zip code level myself cause for us, most of the time the zip code we get is based on the ISP and we end up getting the city business district zip code across the entire city and as per the official documentation ZIP code targeting works for US, Germany and Canada only (I am in Australia)
Cheers,
Abhinav