This is a known iOS issue. Here's the fix:
Force close Settings (swipe up from bottom, swipe Settings away)
Wait 10 seconds, then reopen Settings > Mobile Data
Check if eSIM appears in your SIM list
If YES but not working → Enable Mobile Data + Data Roaming for it
If NO -> use manual entry: tap "Enter Details Manually" in the Add eSIM screen and copy the activation details from your email.
iPhone 14/15: try enabling Airplane Mode before scanning, scan while in Airplane Mode, then turn it off.