If you are logging in to your gmail account from a new application or device, Google might be blocking that device. Try following these steps:
To protect your account, Google might make it harder to sign in to your account if we suspect it isn’t you. For example, Google might ask for additional information besides your username and password if you are traveling or if you try to sign in to your account from a new device.
Go to https://g.co/allowaccess from a different device you have previously used to access your Google account and follow the instructions. Try signing in again from the blocked app.