Unable to access Ops manager using pubic API

Hello,

I am trying to connect ops manager using public API for the first time and getting below error. Please help me to fix this issue.

curl --user '{XXX}:{XXX}' --digest --header 'Accept: application/json' --include --request GET ":/api/public/v1.0/groups?pretty=true"

Content-Type: application/json
Content-Length: 106

{ "reason" : "Unauthorized", "error" : 401, "detail" : "You are not authorized for this resource." }

Thanks!!