“Unable to activate”

So I just drove over an hour to the nearest apple store for them to restore my phone (iPhone XR)because it wouldn’t update to ios15 (I tried to do it on my own very old computer that is running an expired version of windows 10 but was unsuccessful) they were able to restore it. When I got home and tried to set it up again it’s now saying “Unable to activate, An update is require to activate your iphone”

Help!