It seems like your websites hosted on a German server with Pixelx aren't working on the Airtel network but are fine on others. You might want to contact Airtel's customer support to check if there's any restriction on your server's IP. Also, review your server's firewall and security settings to ensure Airtel's IP range isn't being blocked. Running a tracert or traceroute can help pinpoint where the connection is failing. Finally, double-check your DNS settings to make sure everything is set up correctly.