Hi Sweetynewb , good time...
you can try this strategy:
*** In Server side ( Code-Behind file / .cs file )
protected void BtnSubmit_clicked (object sender , eventargs e)
{
if ( size is okay)
else
{
string str = "fn_radio();";
ClientScript.RegisterStartupScript(this.GetType , "myScript" , str , true);
}
}