Email Migration Error

I'm trying to migrate my users from G-Suite to Office 365. In the Admin portal > Setup > Data Migration, I select "Other Email Sources" and enter the following:

IMAP Server Name: imap.gmail.com

Port: 993, SSL

Email Address: [user@domain.com]

Password: [password for above email account]

When I click Save, I get the following error:

"IMAP server check failed, reason: cannot communicate with the datacenter servers."

I've ensured that IMAP is enabled for the accounts and "Allow less secure apps" is turned on.

What am I missing?