Add the plan
Update nothing in a panic. On One UI the path is Settings, Connections, SIM manager, Add eSIM. Scan the QR from the email. If the camera fails, choose enter activation code and use the LPA string from the same email. Samsung sometimes asks you to confirm which SIM is for mobile data immediately. Choose the new one only when you are ready to start the plan in Vietnam. Until then you can leave mobile data on the home SIM so the install itself stays on Wi-Fi.
After you land
- SIM manager: Vietnam eSIM turned on.
- Mobile data: the Vietnam SIM. Turn off “switch to the other SIM for data” if One UI offers a smart toggle.
- Data roaming: off on the Vietnam SIM.
- Preferred SIM for calls: home. Preferred SIM for text messages: home.
- Wait five to ten minutes outside the worst of the terminal concrete.
Galaxy menus move between One UI 5, 6, and 7, but the three facts do not: the eSIM must be on, it must be the data SIM, and roaming must be off. If bars appear and Chrome spins, open Access Point Names for that SIM. The Viettel internet APN is v-internet. Username and password stay empty. Reset to default if you typed a username by habit from another country. A saved VPN or Private DNS set to a hostname that does not resolve will also look like a dead SIM. Set Private DNS to Automatic while you test.
Regional hardware
Samsung sells the same Galaxy S name with different radios. S20+ and later flagships are the models we treat as eSIM-capable, and even those have China and some Hong Kong variants without an EID. A model list goes stale, so this site does not keep one. The dialer code is the decision. If *#06# shows only IMEI, a Viettel QR cannot install, and a counter physical SIM is the honest backup. Write to us if you bought before checking. Say the model number from Settings, About phone, not only the marketing name.
Hotspot is Settings, Connections, Mobile Hotspot and Tethering. It uses the data SIM’s allowance, which is 5GB of high-speed data and then nothing until 23:59 Vietnam time. If the Galaxy says hotspot is on but the 5GB is gone, the laptop will associate to Wi-Fi and still have no internet. That is the plan cap, not a Samsung bug.
One UI also has a data-saver and a “mobile data only for selected apps” list. If Chrome works and Grab does not, Grab may be blocked from mobile data. Allow the apps you actually travel with. That is a phone restriction, not a Viettel one. After any of these changes, give the radio a minute. Repeated SIM off-and-on cycles in a weak hall make registration slower, not faster.