Bank apps usually fail abroad for three reasons: the login comes from an unexpected country (the IP), the one-time code is sent by SMS to a SIM that isn't receiving texts, or the bank wasn't told about the trip. Keep your home SIM active for texts, tell your bank, and use an eSIM whose IP exit your bank accepts.
1. The bank sees a strange country
Fraud systems watch where logins come from. If your travel eSIM exits through a country you have never visited, the bank may block the session or ask for extra checks.
Fix: choose an eSIM whose IP exit is your home country or the country you are visiting. On Flex you pick it before you buy.
2. The code arrives by SMS
Most travel eSIMs are data only. Your bank still texts your home number. Keep your home SIM switched on for calls and texts (turn its data roaming off to avoid charges) and use the eSIM for data. Phones with eSIM support both at once.
Even better: switch the bank to in-app approval or an authenticator before you leave.
3. The bank wasn't told
Some banks still flag card payments abroad. Add a travel notice in the app if your bank offers one, and save the bank's international phone number offline.
A quick checklist before you fly
Update the bank app and log in once at home. Turn on in-app approvals. Keep your home SIM active for texts. Pick an eSIM IP exit your bank expects. Carry a second card from a different bank.