When GVO has MFA switched on (either Optional, Suggested or Required) then users will need to use an 'Authenticator' App to register and then sign in using MFA.
There are a number of Authentication Apps - suggested ones include Google Authenticator, Microsoft Authenticator, Authy or even the in-built authenticator on Apple devices.
Before you can access GVO with MFA switched on you will need to have an authenticator set up on your device (smartphone, PC, tablet, iPad).
Google Authenticator
Microsoft Authenticator
Authy
Each Authenticator will have different set-up requirements so just use the one that is most convenient for you. You may already be using one of these for accessing other platforms and services.
Please contact the GVO Support Desk 0n 01273 921066 if you need any advice.