skype for business showing error KB2566790.

I purchased Ms office 2019 pro plus and got skype for business. when i tried to login first time through my hotmail account their it shows an error written " Skype for business couldn't find a skype for business server for hotmail.com. there might be an issue with the domain name system (DNS) configuration for your domain. see KB2566790 for detail and contact your system admin".

But i just want to use it for online teaching. 

how i can resolve the above problem.