i need to allow youtube for specific user in web policy we are using ip based policy.so please help me .

Hello satyabrata bastia ,

Thank you for reaching out to the community, Please follow the steps below:
1.) Web > Categories > create a custom category:
 
2.) Web > Policy > create a custom policy and allow a YouTube category for a single user only:

after i try with above procedure its not working we are currenly using ip based policy not userbased 

Can you share a screenshot of the FW rule you created ? 

Can you scroll down and share that part of the FW rule too..?

Have you created a LINKED NAT in this rule ?

yes 

Please share the diagnostic packet capture > Monitor traffic using Packet Capture Utility : https://support.sophos.com/support/s/article/KB-000035761?language=en_US

To understand the traffic flow! 

Can you check under the General Policy if video hosting category is blocked ?

Can you check under the General Policy if video hosting category is blocked ?