I can't get the access token

https://backstage.taboola.com/backstage/oauth/token. I clicked on this webpage and was asked to enter my account and password, but after I entered them, it kept popping up again and again, asking me to enter my account and password again. So I have never been able to successfully enter the webpage, and I can't get the token. What should I do?

In addition, I would like to ask, the token is valid for 12 hours. Do I only have 12 hours to complete the connection, or do I have to get a new token and connect again after 12 hours?