What is exact syntax to set flush_param mem_low_wat

I am trying to set 'mem_low_wat ’ and ‘mem_high_wat’
I am using following syntax as per documentation - https://developer.couchbase.com/documentation/server/3.x/admin/CLI/CBepctl/cbepctl-thresholds.html

/opt/couchbase/bin$ sh cbepctl localhost:11210 -b buckethelp -p @password set flush_param mem_low_wat %50

But it is giving following error - Authentication error for buckethelp

I have Admin rights on the bucket.
What is exact syntax for the above command?
Any previlages are required for this?

You have to add “-u @username” juste before you “-p @password

Same goes for all couchbase commands