How to get channelvars variable in through ari

is there a way to enable the optional field of channel…
i tried https://wiki.asterisk.org/wiki/display/AST/Asterisk+16+Channels+REST+API#Asterisk16ChannelsRESTAPI-get and it is giving null

more specifically which ari to call to get linkedid of a channel

The Bridges ARI subsystem might help you find active linked channels:

https://wiki.asterisk.org/wiki/display/AST/Introduction+to+ARI+and+Bridges