For an Explicit Panel that uses a widget, is there a reason the Widget API can't be used to complete an ajax POST?

I am implementing an Explicit Panel, and I was having trouble with using a velocity file as a json url POST endpoint which typically works fine on other pages and provides results from the widget api. When posting from Panels, is it required to use the REST Api when using Panels? if so, why?

Velocity code that is not working as expected in "CoriaMapManPanel.vm":

#if ($core_v2_page.IsPost)
$core_v2_page.SetContentType('application/json')
#set($options = "%{}")               
#set ($id = $core_v2_utility.ParseInt($core_v2_page.GetFormValue('id')))
#set ($name = $core_v2_page.GetFormValue('name'))
#set ($description = $core_v2_page.GetFormValue('description'))
#set ($urlSafeName = $core_v2_page.GetFormValue('urlSafeName'))
#set ($thumbnailUrl = $core_v2_page.GetFormValue('thumbnailUrl'))
 
#set ($isIndexed = $core_v2_utility.ParseBool($core_v2_page.GetFormValue('isIndexed')))
#set ($group = $core_v2_utility.ParseInt($core_v2_page.GetFormValue('groupId')))
#set ($mapOptions = $core_v2_page.GetFormValue('mapOptions'))
#set ($mapTypeId = $core_v2_utility.ParseGuid($core_v2_page.GetFormValue('mapTypeId')))
#set ($mapGuid = $core_v2_utility.ParseGuid($core_v2_page.GetFormValue('mapGuid')))
#set ($createdByUser = $core_v2_page.GetFormValue('createdByUser'))
#set ($modifiedByUser = $core_v2_page.GetFormValue('modifiedByUser'))
#set ($createdUtcDate = $core_v2_utility.ParseDate($core_v2_page.GetFormValue('createdUtcDate')))
#set ($modifiedUtcDate = $core_v2_utility.ParseDate($core_v2_page.GetFormValue('modifiedUtcDate')))

$options.Add('Id',$id)
$options.Add('Name', $name)
$options.Add('Description', $description)
$options.Add('isIndexed', $isIndexed)
$options.Add('group', $group)
$options.Add('mapOptions',$mapOptions)
$options.Add('mapTypeId',$mapTypeId)
$options.Add('mapGuid',$mapGuid)
$options.Add('createdByUser',$createdByUser)
$options.Add('modifiedByUser',$modifiedByUser)
$options.Add('createdUtcDate',$createdUtcDate)
$options.Add('modifiedUtcDate', $modifiedUtcDate)

 
 
#set($response = $context.Update($options))
#if($response.HasErrors())
$core_v2_page.SendJsonError($response.Errors)
#end

#set ($map = $coria_v1_map.Get("%{Id = $id}"))

{"success":true, "redirectUrl":"$map.Url"}
 
#end 

Here is the ajax post that uses it, which has an empty string for the "updateUrl" variable:

/**update is error out because the "context.updateUrl" is "" */
update: function (context, options) {
            return $.telligent.evolution.post({
                url: context.updateUrl,
                dataType: 'json',
                data: options,
                async: true
            });
        },

UpdateUrl is defined as below:

updateUrl : '$core_v2_encoding.JavascriptEncode($core_v2_widget.ExecuteFile('CoriaMapManPanel.vm'))'

so this snippet is called when the panel is loaded, and here is the javascript that the above is embedded in:

<script type="text/javascript">
jQuery(document).ready(function(j){
        j.coria.map.panel.ui.register({
            saveTemplateId : "saveTemplateId",
            fieldItemTemplateId: "fieldItemTemplateId",
            fieldInputListId: '#$core_v2_encoding.JavascriptEncode($fieldInputListId)',
            /**here is the updateUrl that is returned**/
            updateUrl      : '$core_v2_encoding.JavascriptEncode($core_v2_widget.ExecuteFile('CoriaMapManPanel.vm'))',
            redirect       : #if ($redirect) true #else false #end,
            groupRedirect  : '$core_v2_encoding.JavaScriptEncode($core_v2_page.AbsoluteUrl($core_v2_groupUrls.Group($context.MapBook.Group.Id)))',
		        groupId        : '$mapbook.Group.Id',
		        mapbookId      : '$mapbook.ObjectId',
		        applicationKey : '$mapbook.SafeName',
		        groupName      : '$mapbook.Group.Name',
                mapObjectId    : '$map.MapId',

This "$core_v2_page.IsPost" is false. so, maybe I am using this incorrectly...