I have the same issue today. First it said my secondary authentication number didn't work, so I tried to sign in. Then I did "go to bank" and was able to sign in to Venmo fine. Tried to sign in again, nope.

It's annoying that I have to get an authentication code each time, so I only do Venmo at month end. Fortunately it is for my husband's account and not a client! Now this added mess.