This url falls under the category of "Streaming Media".
I see the following Options.
Security & SD-WAN >Content Filtering > Blocked website categories > Streaming Media
Security & SD-WAN >Content Filtering > Blocked URL patterns > o2tvseries.com
Security & SD-WAN > Firewall > Layer 7 Firewall rules > Deny HTTP hostname > o2tvseries.com
You may test the above settings and apply the desired ones.
This can be applied globally or we may create a group policy (Network-wide > Group Policies) and apply to the respective client.
If you have already created a "Group Policy" and applied it on devices.
Please cross check the "MAC Address" + Applied "Policy" on the device under Network-wide > Clients.