This issue may raise because of Salesforce 2-step authorization.
First of all, keep in mind that you must have API access to your Salesforce account for automatic migration.
So, ensure that Salesforce API key is enabled or follow up this advice to turn it on:
- How Do I Enable API Access in Salesforce Classic by the Permission Set?
- How Do I Enable API Access in Salesforce Lightning Experience by the Permission Set?
- How Do I Enable API Access in Salesforce Classic or Lightning Edition (for Contact, Group or Professional editions)?
If you did not turn on Salesforce API key before starting the migration, you would have to do that while authorizing to launch demo.
So, your Demo Migration will be paused till the API token will not be enabled.
After that, come back and press “Authorize” button.
Now, your Migration will continue from the point it was stopped.