REST API for setting Multiple users people picker in SharePoint

Question

I inherited a custom application from another developer who used REST API to create list items. Now the requirement is to add a multiple users people picker to the form.

I am able to add a multiple people picker to the form. However when I am trying to save I get this error "A node of type 'startArray' was read from the JSON reader when trying to read a value of property; however, a 'PrimitiveValue' or 'StartObeject' node was expected"

I understood from other blogs that the syntax should be "RequestorId": { "results": [106,111] }. But my problem in my code is to have this value in a variable and then push into an array and pass it into the function which does the creation of an item. What I am struggling here is the syntax for that variable.

Should I include the curly brackets as well {}

var    colsAndValues = [];  
var   peoplepicker1 = SPClientPeoplePicker.SPClientPeoplePickerDict.elvlglENotification_TopSpan;
                             if (peoplepicker1 != null) {
                      var users = peoplepicker1.GetAllUserInfo();
                        if (users.length == 0) {
                       //alert("No users");
                    //    Mutiple User/Lookup value format:   {FieldName: {"results": [LookupIdVal1,LookupIdVal2] }}

                        colsAndValues.push("RequestorId");
                        var UserValue =  "'results'"+":[0]";// Not sure if this is right syntax. Here is where I feel my problem is

                        colsAndValues.push(UserValue);
                    }

//Function for creating the list item

var item = {
                    "__metadata": { "type": itemType }
                };
                for(var i = 0; i < colsAndValues.length; i++) {
                    if (i % 2 !== 0) {

                        item[colsAndValues[i-1]] = colsAndValues[i];
                    }
                }
                var siteurl = _spPageContextInfo.webAbsoluteUrl;

                jQuery.ajax({
                    url: siteurl + "/_api/web/lists/getbytitle('" + listName + "')/items",
                    type: "POST",
                    contentType: "application/json;odata=verbose",
                    data: JSON.stringify(item),
                    headers: {
                        "Accept": "application/json;odata=verbose",
                        "X-RequestDigest": jQuery("#__REQUESTDIGEST").val()
                    },

Answer 1

We can use the REST API to get UserId of all the users in the people picker field, then pass field data as below to add item using REST API.

"RequestorId": { "results": userIds}

The following example code for your reference.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>  
<script type="text/javascript" src="_layouts/15/clienttemplates.js"></script>  
<script type="text/javascript" src="_layouts/15/clientforms.js"></script>  
<script type="text/javascript" src="_layouts/15/clientpeoplepicker.js"></script>  
<script type="text/javascript" src="_layouts/15/autofill.js"></script>

<div>
    <label>User Name:</label>  
    <div id="elvlglENotification"></div>
    <div><input type="button" value="Save" onclick="addToList()"></input></div> 
</div>
<script type="text/javascript">
$(document).ready(function() {  
    initializePeoplePicker("elvlglENotification");  
});  
function initializePeoplePicker(peoplePickerElementId) {  
    var schema = {};  
    schema['PrincipalAccountType'] = 'User,DL,SecGroup,SPGroup';  
    schema['SearchPrincipalSource'] = 15;  
    schema['ResolvePrincipalSource'] = 15;  
    schema['AllowMultipleValues'] = true;  
    schema['MaximumEntitySuggestions'] = 50;  
    schema['Width'] = '280px';  
    this.SPClientPeoplePicker_InitStandaloneControlWrapper(peoplePickerElementId, null, schema);  
}
function addToList(){
    var userIds=[];
    var peoplePicker = this.SPClientPeoplePicker.SPClientPeoplePickerDict.elvlglENotification_TopSpan;
    // Get information about all users.
    var users = peoplePicker.GetAllUserInfo();
    for (var i = 0; i < users.length; i++) {
        var accountName=users[i].Key;
        var userId=GetUserId(accountName);
        if(userId!=-1){
          userIds.push(userId);
        }           
    }
    var listName="CL0801";
    var itemType = GetItemTypeForListName(listName);
    var item = {
        "__metadata": { "type": itemType },
        "RequestorId": { "results": userIds}
    };  
    $.ajax({
        url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('" + listName + "')/items",
        type: "POST",
        contentType: "application/json;odata=verbose",
        data: JSON.stringify(item),
        headers: {
            "Accept": "application/json;odata=verbose",
            "X-RequestDigest": $("#__REQUESTDIGEST").val()
        },
        success: function (data) {
            alert('Success');           
        },
        error: function (data) {
            alert("Error");
        }
    });
}
function GetUserId(accountName){
    var userId=-1;
    /// get the site url
    var siteUrl = _spPageContextInfo.siteAbsoluteUrl;
    /// make an ajax call to get the site user
    $.ajax({
        url: siteUrl + "/_api/web/siteusers(@v)?@v='" +encodeURIComponent(accountName) + "'",
        method: "GET",
        async:false,
        headers: { "Accept": "application/json; odata=verbose" },
        success: function (data) {
            userId=data.d.Id;
        },
        error: function (data) {
            console.log(JSON.stringify(data));
        }
    });
    return userId;
}
function GetItemTypeForListName(name) {
    return "SP.Data." + name.charAt(0).toUpperCase() + name.split(" ").join("").slice(1) + "ListItem";
}  
</script>