This error appears for one of two reasons. Either when the eSIM is installed fully or partially on a device already.
Usually the install will go successfully, even if the device locks it will often continue in the background on newer devices. Rescanning the QR code will give this error often meaning it is already installed. Check through your settings to see if it is already there.
Annak az ellenőrzése, hogy az eSIM már telepítve van-e:
Nyisd meg a Beállítások > Általános > Névjegy menüpontot