Unable to login on my website

Our users are unable to login from some places and if we use their credentials it works but they cannot login to the system.

Via Access? On which website? What error does that give them?

We have a dashboard page where we input the data. The problem is after we implemented the cloudflare it started giving unauthorized request error. But the username and passwords are right. If I try to login from my system it works but if other person is trying from other country it gives unauthorized request error