You do pass the ID of the page there, just like it says in the documentation… but you said you were using pages/{id} in the path URL, which is an invalid path. If you are now saying you are using content/{id} in the path URL, then that is a valid path and should work.
You need to provide a COMPLETE description of the problem. Refer to the How to ask a good question thread for a better understanding of the minimum level of information you need to provide.
And I have no idea whatsoever what ‘SLB-Private’ means.