[Freeswitch-dev] Cannot update a Channel Variable inside the api_hangup_hook lua script

Hi Freeswitch Experts, I am using session_in_hangup_hook = true and api_hangup_hook to call my lua script where I want to change the value of my channel variable through session:setVariable("custom_channel_variable", "new_value"). But I can see that I cannot do that. It is not getting changed. I am able to access the channel variables through session:getVariable("custom_channel_variable") but I cannot set them after the call is hung up. How can I do that? If I cannot do that then what is the reason? I do not see any reason yet in the Freeswitch documentation. Can anyone enlighten me over this? Thanks and Regards Varun Singh