xml, google script c#

I try to register the script below, and show on default.aspx

the codes look right but don't work to me. Please help.

protected void Page_Load(object sender, EventArgs e)
{
	string googleScript = string.Empty;
	if (domainName.Contains("aaa.com"))
	{
	 googleScript = "<script async src='https://www.googletagmanager.com/gtag/js?id=UA-923423499-4'></script>" +
               "<script> window.dataLayer = window.dataLayer || []; " +
               " function gtag(){ dataLayer.push(arguments); } " +
               " gtag('js', new Date()); " +
               " gtag('config', 'UA-923423499-4'); " +
               "</script>";
	}
	if (googleScript != "")
        {
                Page.ClientScript.RegisterStartupScript(this.GetType(), googleScript,"",true);
        }
}

//my goal is to add <script></script> on aspx webpage

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