The eSIM is compatible with iPhone Xs, iPhone Xs Max or iPhone XR devices running iOS 12.1 or later. Your device must also be unlocked.
When you buy a device with a contract from a mobile operator, it is common practice for them to lock the connectivity from any other supplier. In this case, your device will be considered "locked"—at least until your contract expires. You can check with your operator to see if there is anything you can do to unlock the eSIM in your device.
Some mobiles of iPhone Xs, iPhone Xs Max or iPhone XR purchased in China and Hong Kong are not eSIM compatible however do have 2 physical SIM slots. United Networks can provide a physical SIM for these devices