Messages like "Cellular Plan Cannot Be Added" or "Unable to Activate eSIM" nearly always mean one of four things — and only one of them is about the eSIM itself
The Four Causes
- The phone is carrier-locked. The chip is there and the operator will not allow anything else onto it — check Settings › General › About › Carrier Lock on an iPhone
- There is no internet connection. Installing downloads a profile; without Wi-Fi or data there is nothing to download from
- The code has already been used. A profile installs once
- There is no room. The phone holds a limited number of profiles, and old ones may need deleting first
Work Through It
- Confirm you are on Wi-Fi and it actually reaches the internet — open a web page to be sure
- Check the carrier lock, and contact whoever sold the phone if it is locked
- Look in the settings for a line already carrying the destination's name
- Restart the phone and try once more
- Try manual entry rather than the QR code
- Check the phone's software is up to date
A carrier-locked device is one of the situations excluded from the Refund Policy, because the plan was delivered correctly. It is worth checking the lock before buying — see Is My Phone Carrier-Locked, and How do I Check?
If none of that helps, contact support with the exact wording of the message and a screenshot. The message text is what tells us which of the four it is
