不确定为什么我的AJAX调用不能在webforms中填充数据

<script src="https://ajax.aspnetcdn.com/ajax/4.0/1/MicrosoftAjax.js" type="text/javascript"></script>
<script src="https://ajax.aspnetcdn.com/ajax/mvc/3.0/MicrosoftAjaxMvc.js" type="text/javascript"></script>

<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <!-- 需要更新的内容 -->
    </ContentTemplate>
</asp:UpdatePanel>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <asp:Button ID="btnSubmit" runat="server" Text="提交" OnClick="btnSubmit_Click" />
    </ContentTemplate>
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="btnSubmit" EventName="Click" />
    </Triggers>
</asp:UpdatePanel>

protected void btnSubmit_Click(object sender, EventArgs e)
{
    // 处理数据
    string data = "需要填充的数据";

    // 返回数据给前端
    ScriptManager.RegisterStartupScript(this, GetType(), "FillData", $"FillData('{data}')", true);
}