The example for db.cloneCollection() at the page https://docs.mongodb.com/manual/reference/method/db.cloneCollection/ stated:

db.cloneCollection('mongodb.example.net:27017', 'users.profile',
                    { 'active' : true } )

The users.profile collection name is incorrect, since currently the db.cloneCollection() function auto-appends the current database name (https://github.com/mongodb/mongo/blob/v3.4/src/mongo/shell/db.js#L382).

The correct example should be (assuming we are in the users database):

db.cloneCollection('mongodb.example.net:27017', 'profile',
                    { 'active' : true } )