Unable to track iPhone SE in FindMy as it shows “location not found”

Hi! I recently replaced my 13 yo son’s lost iPhone 12 with an iPhone SE. When I go to “find my” to track him on my phone, it says “locating…” and then it says “location not found” I have turned on location services, his iOS is up to date, and I’ve gone through all the basic steps I’ve found when I google this issue. What am I missing? Is there any security setting that needs to be disabled?

[Re-Titled by Moderator]