I can't sign in to my second Gmail account from my phone. My username & password are correct. They work on my laptop. I successfully changed my password online. Gmail is constantly giving me notifications saying: "Credentials Needed." I can send & receive messages from my main account.
I am using the updated gmail app. The security page says I am using an insecure app.
My mobile phone, an LG Nexus 5 running Android 6.0.1 is not listed as a trusted device. The only way to add it to the list is to sign in with it, but I can't. I have been using it on this phone for years! Any idea why is this happening?