I had the error above because I tried to use an username and password for another account, my bad . I was able to fix it by logging into my ouath account and using the cookies to get the session key. Is there a way I can get my account a username and password?
I'm glad you figured this out. For the moment it's not possible to get a password and username, but it's in our plans. We'll update you here when this is the case.
User session tokens are one of two ways to authenticate with the Migration API.
You can also use a permanent token to authenticate, which will let you to avoid the complications you ran into with the session token when you log into Prismic via OAuth or SSO.