Moodle rest post returning error with feature core_user_get_users_by_field - web-services

Question

Hi I'm new with moodle and I'm getting an error when calling the webservice.
Currently I'm trying to retrieve a user from moodle with the following function core_user_get_users_by_field and I'm using rest service to do so. I already managed to create a user thus I am authenticated to use the service.
the error that I'm receiving is
Missing required key in single structure: field
The bellow is the code was used to create a User. the issue that I got from the error is that the parameter that I need to send for the post is not formatted well. Does anyone know how to search correctly with this method or any other method.
String token = "token";
String postData = "username=username";
string createRequest = string.Format("http://domain/webservice/rest/server.php?wstoken={0}&wsfunction={1}&moodlewsrestformat=json", token, "core_user_get_users_by_field");
// Call Moodle REST Service
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(createRequest);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
// Encode the parameters as form data:
byte[] formData =
UTF8Encoding.UTF8.GetBytes(postData);
req.ContentLength = formData.Length;
// Write out the form Data to the request:
using (Stream post = req.GetRequestStream())
{
post.Write(formData, 0, formData.Length);
}
// Get the Response
HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
Stream resStream = resp.GetResponseStream();
StreamReader reader = new StreamReader(resStream);
string contents = reader.ReadToEnd();
// Deserialize
JavaScriptSerializer serializer = new JavaScriptSerializer();
if (contents.Contains("exception"))
{
// Error
MoodleException moodleError = serializer.Deserialize<MoodleException>(contents);
}
else
{
// Good
}

Answer 1

The webservice core_user_get_users_by_field needs an associative array given as parameter with the following key:values
'field': 'id'
'values': array of integers (must be an array, possibly with just one value)
In PHP it would be, for example:
$parameters = array('field' => 'id', 'values' => array(13));
It means: the user whose 'id' has the value of 13. Of course, you can use other parameters as well: ('field'=>'lastname', 'values'=> array('Smith'))
The parameters you can choose are the fields of the Moodle 'user' table.
Try to build these parameters in your postData variable.

Answer 2

Here's URL that work with my put this url in postman and set http method to post method
hostname/webservice/rest/server.php?wstoken=any_token&wsfunction=core_user_get_users_by_field&field=email&values[0]=h#fci.com
&moodlewsrestformat=json