setChannelVar throwing an error in ARI


I am using official [ARI python code](
when i am trying to use setChannelVar: POST /channels/{channelId}/variable function as channel.setChannelVar('lastVal', 'here'), I am getting the error

TypeError: enrich_operation() takes exactly 0 arguments (2 given)

but when I see the [official documentation]( it says this function is supposed to be used like that.
kindly help me figure out what am i doing wrong?
Asterisk - 15.5