I've experienced error 740 while trying to connect my Google account to the Assist app, and I found a solution that worked for me. Apparently, it was a problem with the Google account settings, specifically the 2-step verification. Once I disabled the 2-step verification, I was able to connect my account without any issues. It might be worth trying if you're getting the same error, just make sure to re-enable the 2-step verification once your account is connected.