To avoid being charged by your mobile operator when you are in the roaming zone, we advise you to make sure that your phone uses only MobileXY Mobile Data.
You can easily check this. Go to Settings – Mobile Data/Cellular – Mobile Data – turn off Allow Mobile Data Switching.
If you do not want to turn off the Allow mobile data switching mode, but you do want to know which SIM is using data, go to your device’s Mobile / Cellular Settings and check under Mobile Data. Your device will indicate whether it is using data from the primary SIM (your physical, regular SIM card) or the eSIM. If you have multiple eSIMs installed, your device will also indicate which eSIM it is using by displaying its label – the nickname you chose for your eSIM when it was installed.