Arriving at the airport, turning on the phone but the map cannot be loaded is one of the situations that easily panics first-time visitors to Japan. In most cases, it is not the eSIM that is broken; It's usually just a matter of missing one of a few very small steps. Follow the order below to process in minutes, instead of hastily deleting the eSIM or rescanning the QR.
The phone may still prioritize Vietnamese SIM as mobile data. Go to Mobile/SIM section, select Japanese eSIM as Mobile Data. Keep your Vietnam SIM on if you need to receive SMS/OTP, but turn off its mobile data to avoid unwanted roaming.
Many travel eSIM plans run through partner networks so Data Roaming / Data Roaming needs to be enabled on the Japanese eSIM itself. This is the most overlooked setting. Turn on roaming for eSIM, not for Vietnam SIM.
Turn on airplane mode for about 10 seconds and then turn it off. Then wait one to two minutes for the device to register to the network. Don't change carriers manually right away; to select automatically first.
Go to the SIM/eSIM list, make sure the Japanese eSIM is in the On state. If you install from Vietnam, it is normal for there to be no signal before landing; Please check again once you are in Japan and have roaming turned on.
Do not manually fill in random APNs. Most eSIMs are self-configuring; Only enter the APN if the instructions accompanying the QR or support staff request it. Incorrect typing can make it difficult to know where the error lies.
If you have done the above five steps and still have no network, take a screenshot of the eSIM settings (cover QR/ICCID), device name, current location and error message. This way support can handle things quickly instead of having to ask each step again.
Install the eSIM before your trip while Wi-Fi is available and save the instructions/QR in a safe place. See how to install Japanese eSIM and article keep Vietnamese number to receive OTP before flying. If you have not selected a plan, see Japanese eSIM by number of travel days.
Tip: When you need help, describing "eSIM as data selected, roaming turned on, flight turned on/off" will help support process much faster than just saying "no network".
Detailed instructions on how to maintain a Vietnamese SIM to receive bank OTP codes and application messages when coming to Japan. Tips for using eSIM in parallel to help keep the connection smooth.
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