Error "Unable to connect" when opening the page on SSO

What sample tool are you using?
3.single-sign-on
https://github.com/microsoft/CopilotStudioSamples/blob/master/BuildYourOwnCanvasSamples/3.single-sign-on/index.html

Describe the bug
after editing the page to fill the four variables

• clienID
• authority
• theURL
• "My-custom-prefix"

, I get the following result showing that the copilot can’t connect:

To Reproduce
Steps to reproduce the behavior:

1. Donwload the file https://github.com/microsoft/CopilotStudioSamples/blob/master/BuildYourOwnCanvasSamples/3.single-sign-on/index.html locally
2. Replace the four variables above with the appropriate values
3. Save the page
4. Run a web server (e.g. python -m http.server or a nodejs server that integrates CORS)
5. Open the page

Expected behavior
The authentication window is shown which, instead, does NOT show up; instead, the embedded copilot says "connecting..." for half a second, followed by the "Unable to connect" error

Screenshots
Please check the screenshot above

Additional context

• I followed exactly the same steps indicated in the article https://learn.microsoft.com/en-us/microsoft-copilot-studio/configure-sso?tabs=webApp.
• I also watched this video https://www.youtube.com/watch?v=xk45a4qEM8c where it works, but it's using an older version of the file.
• I tried adding the following instruction at the beginning of "async function main()" as suggested by the article, but the behaviour is the same
  if (clientApplication.getAccount() == null) { await clientApplication.loginPopup(requestObj).then(onSignin).catch(function (error) {console.log(error) }); }
• popups are enabled

Start with BuildYourOwnCanvasSamples/3.single-sign-on/index.html and reproduce the issue using the four documented values and a local web server. Compare the current sample with the linked SSO article and older video, then verify that the authentication window appears and the embedded copilot connects instead of showing "Unable to connect."