When a user states that they will be travelling internationally, check to see if the country or countries are allowed for MS 2FA Authentication.
Logon to the Azure portal - https://portal.azure.com/#home
From the top row, select Microsoft Entra Conditional Access
Expand the Manage folder, select Named Locations
Select Trusted Countries
Important: The countries that are Checked will be Blocked. The countries that are Unchecked are Allowed
Check/Uncheck the appropriate country for the user.
Hit Save