Web services

I am trying to pull user details using core_user_get_users, using email and id it's working OK, but how to use it if I have a additional field "Person No | personno"?

Getting user details by email address: OK

https://imoodle.sm.com/webservice/rest/server.php?wstoken=WSTOKEN&wsfunction=core_user_get_users&moodlewsrestformat=xml&criteria[0][key]=email&criteria[0][value]=paulmcarney@yahoo.com=paulmcarney@yahoo.com

Getting user details by id: OK

https://imoodle.sm.com/webservice/rest/server.php?wstoken=WSTOKEN&wsfunction=core_user_get_users&moodlewsrestformat=xml&criteria[0][key]=id&criteria[0][value]=2953

QUESTION:

But how to get user details using below optional field/User profile fields| Additional Information? => Person Number/personno with value of 210792

<SINGLE>

     <KEY name="type">

          <VALUE>text</VALUE>

     </KEY>

     <KEY name="value">

          <VALUE>210792</VALUE>

     </KEY>

     <KEY name="name">

          <VALUE>Person Number</VALUE>

     </KEY>

     <KEY name="shortname">

          <VALUE>personno</VALUE>

     </KEY>

</SINGLE>

Thanks!