Before login, You must be logged into your Facebook account from your browser first!
If your Facebook Login Two Steps Verification is activated, Please check your notifications and confirm new login device and save, then try to generate the access token.
Uncomfortable login use password facebook, You can Generate Apps Password
and Save your Password Apps.
Now, Every time you can login via your mail/username with Apps Password.
To protect your account, You can only generate your access token once, please save your last access token so you can directly enter your old access token for next time login. You can generate your new access token if your old access token is expired or if you can't login using your old access token.