I can't migrate my gmail account

I can't migrate my gmail account

I've been consolidating my general email addresses into one. The Outlook e-mail thankfully worked after some struggle. Gmail keeps giving me a 

Authentication details provided was rejected by Source server. Kindly provide valid username and password.

I did accept the IP when it prompted me in Gmail. It was still a no go, which has left me very much drained on the subject after more than a dozen retries.