If not using administrative authentication, then an OAuth 2.0 CHALLENGE requires user actions in order to authorize MigrationWiz to ACCESS their data. After submitting a migration for mailbox(es), MigrationWiz will send an email to each user mailbox in order to ask for access privileges. Once the user confirms access privileges, their migration will begin.

Note: 

• Non-paid Google account migrations will also follow the above OAuth 2.0 challenge methodology. It is necessary to migrate these accounts using the individual user name and PASSWORDS for each account.
• Previously Google USED "ClientLogin" for such migrations. This has been deprecated and replaced by OAuth 2.0.

Here are some more generic (non-specific to MigrationWiz) questions and answers about OAuth and OAuth 2.0. These have been included here to provide some more detail about how it works.

If not using administrative authentication, then an OAuth 2.0 challenge requires user actions in order to authorize MigrationWiz to access their data. After submitting a migration for mailbox(es), MigrationWiz will send an email to each user mailbox in order to ask for access privileges. Once the user confirms access privileges, their migration will begin.

Note: 

Here are some more generic (non-specific to MigrationWiz) questions and answers about OAuth and OAuth 2.0. These have been included here to provide some more detail about how it works.