C# Difficulty accessing HTML DOM element

Question

I am trying to access an element from a website, however, it is not returning the complete element.

<div id="playcontainer" class="play bigger isnd">
   <div id="dooplay_player_response"> <!--  -->
      <div class="pframe">
         <iframe class="metaframe rptss" src="https://startflix.net/embedPlay.php ..."> <!-- I want this -->
         </iframe>
      </div>
   </div>
</div>

//Using mshtml.IHTMLDocument3
IHTMLDocument3 dom3 = (IHTMLDocument3)wb.Document.DomDocument;
IHTMLElement idDoo = dom3.getElementById("dooplay_player_response");

//Using System.Windows.Forms.HtmlElement
HtmlElement target1 = wb.Document.GetElementById("dooplay_player_response");

string idDooOuter = idDoo.outerHTML;
string target1Outer = target1.OuterHtml;

both idDooOuter and target1Outer are not returning descendant elements from dooplay_player_response, which would be class="pframe".

I've tried using FindByClassName() features but I can't access this element. My intention is to get the code inside the iframe. Could someone help me with this problem?

Edit: Obs. I tried using other programming languages, such as Java, Python, javascript (Tampermonkey) and C ++, in all the results were the same, I can't get this element.