title: REST HTTP Status Code Best Practice for validation API
body: <p>I am creating a simple API to validate a membership. Client will have to input a String ID and Server will check if the ID is a valid member of our, lets say, community. The ID must be numeric only, with length 10.</p>
  
  <p>Quite simple right?</p>
  
  <p>If the ID is a valid, of course we will return HTTP Status Code OK.
  If the ID is contains alfabet, or less/more than 10, then we will return HTTP Status Code BAD REQUEST.</p>
  
  <p>The question is, what is the best practive HTTP Status Code to return when the ID is numeric and length = 10, but is NOT a member of our community? and why is that.</p>