Is your phone locked to a carrier?
This is the second most common reason a travel eSIM will not work, and the only one that no setting on your side can get around. It is also easy to check before you spend anything.
What "locked" actually means
When a mobile operator sells a phone below its real price and recovers the difference through your monthly bill, it protects that arrangement by locking the handset to its own network. A locked phone will accept profiles from that operator and refuse everyone else’s. It rarely says so plainly: you usually get a vague error, or the profile installs and then never connects to anything, which sends people looking for a fault in the eSIM.
Check on iPhone
Open Settings › General › About and scroll to the line reading Carrier Lock. "No SIM restrictions" means the phone is free and any eSIM will install. Anything naming an operator means it is locked to them. This line is written by the phone itself, so it is the most reliable answer you can get without calling anyone.
Check on Android
There is no single screen, because manufacturers word it differently. Look under Settings › About phone or Settings › Connections for a "SIM lock" or "Network unlock" entry, and if there is none, the practical test is simpler: try installing the eSIM. A locked phone rejects the profile at the point of installation rather than silently later, so you find out immediately and nothing is consumed — our QR code is only spent once a profile actually installs.
Where the phone came from usually tells you
Bought outright from the manufacturer, from a retailer, or second-hand from a private seller: almost always unlocked. Bought on a monthly contract from a mobile operator, or given to you as part of a plan: assume locked until you have checked. Phones bought abroad on a local operator’s deal are the ones that surprise people most often, because the lock travels with the handset.
Getting it unlocked
Only the operator that locked it can unlock it — no app, code seller or shop can do it legitimately, whatever they advertise. Contact them and ask; in most markets they are required to do it free once the device is fully paid off, and the request usually takes a few days rather than minutes. Start this well before you travel, not the week of the flight.