I have used below code its working fine.
var req = new XMLHttpRequest();
req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v9.1/campaignactivities?$select=activityid,subject,_wcl_technicalactivity_value&$filter=_wcl_technicalactivity_value eq '" + newID + "'", true);
req.setRequestHeader("OData-MaxVersion", "4.0");
req.setRequestHeader("OData-Version", "4.0");
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.setRequestHeader("Prefer", "odata.include-annotations=\"*\"");
req.onreadystatechange = function () {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var results = JSON.parse(this.response);
for (var i = 0; i < results.value.length; i++) {
if (results.value[i]["activityid"] !== null)
var activityid = results.value[i]["activityid"];
if (results.value[i]["subject"] !== null)
var subject = results.value[i]["subject"];
if (results.value[i]["_wcl_technicalactivity_value"] !== null) {
var _wcl_technicalactivity_value = results.value[i]["_wcl_technicalactivity_value"];
var _wcl_technicalactivity_value_formatted = results.value[i]["_wcl_technicalactivity_value@OData.Community.Display.V1.FormattedValue"];
var _wcl_technicalactivity_value_lookuplogicalname = results.value[i]["_wcl_technicalactivity_value@Microsoft.Dynamics.CRM.lookuplogicalname"];
}
var value = new Array(); //create a new object array
value[0] = new Object();
value[0].id = activityid; // set ID to ID
value[0].name = subject; //set name to name
value[0].entityType = "campaignactivity"; // entity schema name
if (formContext.getAttribute("wcl_catechnicalactivityattendanceid") !== null)
formContext.getAttribute("wcl_catechnicalactivityattendanceid").setValue(value);