Populate multiple values from 1 entity to another using JS

function populateInvoicingDetails()

{
if(Xrm.Page.getAttribute("customerid").getValue()!=null)

//read

var opportunity = Xrm.Page.getAttribute("customerid").getValue()[0].id;

var opportunityId = opportunity.substring(1, 37);

opportunityId = opportunityId.replace('{', '').replace('}', '');
var req = new XMLHttpRequest();

req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v9.1/accounts(" + opportunityId + ")?$select=new_invoicetocontactname", 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 result = JSON.parse(this.response);

var oppnumber1 = result["new_invoicetocontactname"];

// Replace with the actual field names of the email address and phone number in custom entity

Xrm.Page.getAttribute("new_invoicetocontactname").setValue(oppnumber1);
} else {

Xrm.Utility.alertDialog(this.statusText);

}

}

};

req.send();

}