Save As dialog does not appear

When I press the Save As button, the Save As dialog does not appear!

Where does this problem come from? What should I do in my wopi host?

(The problem is not about CODE, since its docker works properly when I integrate it with nextCloud or ownCloud docker containers)

I notice that when I enter <wopi client ip port>/hosting/capabilities in my browse, I get the following response:

   convert-to: {
      available: true
  hasMobileSupport: true,
  hasProxyPrefix: false,
  hasTemplateSaveAs: false,
  hasTemplateSource: true,
  productName: "Collabora Online Development Edition",
  productVersion: "6.4.8",
  productVersionHash: "4aa2794"

It seems that hasTemplateSaveAs: false says that CODE does not support save as UI, and I should add it myself.
Am I right?

Should I do that with PostMessages?

I detect that I should Use Action_SaveAs post message:

By recieving UI_SaveAs post message, the following code is executed:

function handlePostMessage(event, iframeRef){
    const msg = JSON.parse(;
    if(msg.MessageId === 'UI_SaveAs'){
        const msg2={
                "Values": {
                    "Filename": 'testname.txt',
        iframeRef.current.contentWindow.postMessage(JSON.stringify(msg2) ,'*');

but it did not send any post messages to collabora.

Could someone help me please?