Step 1
Include the below function to onLoad in the form
function RunMembershipPaidProcessDialog()
{
//Set the process dialog Id below
var dialogID = "%7b706886CB-FFAB-4ECC-967E-B457CBE8C2C1%7d";
//Set the entity logical name
var entityName = Xrm.Page.data.entity.getEntityName();
//Get the current record Id
var recordId = Xrm.Page.data.entity.getId();
//Set the Process Dialog width & height
var width = "550";
var height = "450";
LoadProcessDialog(dialogID, entityName, recordId, width, height);
}
Step 2
Create a Common Javascript resource file (if you havn't create yet) so you can add all the common javascript function in this web resource.
and add the below function
function LoadProcessDialog(dialogID, entityName, recordId, width, height)
{
var context = Xrm.Page.context;
var sUrl = window.parent.location.href;
sUrl = sUrl.substring(0, sUrl.indexOf('/main.aspx'));
var fullUrl = sUrl + "/cs/dialog/rundialog.aspx?DialogId=" + dialogID + "&EntityName=" + entityName + "&ObjectId=" + recordId;
ShowPopUpWindow(fullUrl, "newWindow", width, height);
}
function ShowPopUpWindow(url, title, w, h)
{
var left = (screen.width/2)-(w/2);
var top = (screen.height/2)-(h/2);
var targetWin = window.open(url, title, 'toolbar=no, location=no, directories=no, status=no, menubar=no, scrollbars=no, resizable=no, copyhistory=no, width='+w+', height='+h+', top='+top+', left='+left);
}