When google won’t let me sign in on the phone or computer. it means, something is wrong with the user account settings, or server. So here are the guide to fix it on your device.
When Gmail is not working on the phone or computer. you should check the username and password for your Gmail account. make sure that the password is correct. In case, if you are not sure about it. you can reset the password and then retry to access the account with new password.
If you are seeing the temporary error during the google account sign in period. You should refresh the Gmail login page. if the error still continues. it means, there is an issue with the Google server. so you need to wait until they will resolve it.
Sometimes, users are unable to access the google account because of the browser or mail application issue. so you should optimize these applications. After that, you should try to access the mailbox again.
If gmail is not working on the mail application while it is working fine on the other browsers. you should check the imap and pop3 server settings. make sure that the pop3 server settings are working perfectly fine.