You land, you wait for the seatbelt sign, you look down at your phone, and instead of a network name you get two words with the emotional weight of a slammed door: No service. Before you conclude the eSIM is broken, work through this list in order - the fix is almost always one of five settings, and almost never the eSIM itself.
It helps to know why this happens at all. A travel eSIM install and a travel eSIM working are two different milestones, separated by a handful of small toggles your phone doesn't turn on automatically, mostly for good reason - you wouldn't want your phone racking up roaming charges on a line you never intended to use abroad. The list below runs through those toggles in the order most likely to be the culprit, quickest checks first.
Check the basics first
1. Is the line actually switched on? Sounds too obvious to mention, and is nonetheless the most common cause. Go into your SIM or Mobile Service settings and check the travel eSIM line is toggled on, not just installed. Installing a profile and activating it are two separate steps on both iPhone and Android, and it's easy to complete the first without noticing you skipped the second.
2. Is it actually your data line? Your phone needs to be told which line handles mobile data - if that setting is still pointed at your home SIM, your travel eSIM can be perfectly installed and completely idle. Check Mobile Data (iPhone) or the mobile data toggle in SIM settings (Android) and confirm it's set to the travel line, not the home one.