Getting error while message search

Im using UI kit 2.7.1
there im trying to use message search in group channels
i followed doc
and i’ve turned on message search feature in dashboard
when i try to hit this
im getting response as below

{"error":true,"message":"\"GET Search Message\" failed.","code":500901}

if I remove channel_url and custom type im getting response as
Although i have the search keyword in channels.

can any one please help here?