First, verify that the same credentials work to log into the Qobuz account web page directly via a browser on this same network.
Log out fully from that page. Navigate to Settings → Services within Roon and make sure you’ve fully signed out of all streaming services.
Restart RoonServer and then attempt to log in via Settings → Services under the Qobuz tab.
If that doesn’t help, then enter your router settings page and verify that a reliable DNS server has been assigned in the “DNS” tab or similar. We often recommend Cloudflare (1.1.1.1) or Google (8.8.8.8) as the assigned server, since they can reliably resolve the addresses relevant to Qobuz’s API in Roon.
If you created your Qobuz account via Facebook/Google/Apple accounts, see here: