This is the problem you are having with Response.The way the path is being resolved in the IIS environment is probably the cause of Redirect's incorrect inclusion of the myApp root folder in the URL. Here's how to make it right:

1. 1. Use.Reroute
ResolveUrl ensures that the myApp folder is included in the URL by assisting in determining the right path based on the application root.

protected void Test_RedirectSSM(object sender, EventArgs e)
{
    string url = ResolveUrl("~/UserPages/TestareSSM.aspx");
    Response.Redirect(url);
}

2. Use Request.ApplicationPath
Another approach is to manually build the URL using Request.ApplicationPath, which will ensure that the application’s root folder (myApp) is correctly prefixed in the URL.
protected void Test_RedirectSSM(object sender, EventArgs e)
{
    string url = $"{Request.ApplicationPath}/UserPages/TestareSSM.aspx";
    Response.Redirect(url);
}

3. Absolute Path
If you are dealing with a situation where you must use an absolute path, ensure you correctly structure it, including the full application path:

protected void Test_RedirectSSM(object sender, EventArgs e)
{
    Response.Redirect("https://iis/myApp/UserPages/TestareSSM.aspx");
}

Summary
ResolveUrl("~/...") is often the most reliable and easiest way to ensure URLs are correctly resolved relative to the application root.
Request.ApplicationPath can be used to dynamically construct paths based on where your application is deployed.
Ensure that any absolute URLs used include the entire path, including the myApp portion.

These approaches should help ensure that the redirect URL correctly includes your application's root folder (myApp) when deploying on IIS.