Hi Deneb,
According to the error message you encountered, this issue is probably caused by the DNS settings for Lync online service.
If you’re using Office 365 for Enterprises, I suggest you follow these steps to check your DNS settings:
1. Sign in to the Office 365 Admin Center and click domains in the left panel.
2. Select your current domain name and click Troubleshoot.
3. Select I changed the settings at my provider more than 72 hoursago if you did.
4. Click Next.
Then you’ll see if there is anything incorrect with the DNS settings of your current domain.
If you’re using Office 365 post-upgrade, you can directly click Manage your website and email domains under domains section in the Office 365 Admin Center.
Moreover, it is recommended you refer to the following link to find the correct DNS settings for Lync online service:
Troubleshooting Lync Online DNS configuration issues in Office 365
Thanks,
Allen Zhang