What am I doing wrong with this function?

Here's my sql: SELECT sum (allocatedamount) as capxtotal from cer_Capx where cermodelid=@ModelID

Here's how I'm documenting it as a function:

   if(!function_exists('cer_capxsum')) {
        function cer_capxsum($mID) {
         global $edb, $_SESSION;
         
         $sql_data = "exec cer_CapxSum $mID";
          if ($_SESSION["portaladmin"] == 1 && $_SESSION["showsql"] != "no")
            echo display_detail("cer/cer_functions.php",$sql_data);
        $result_data = odbc_exec($edb, $sql_data);
         }  
    }
     

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Here's how I'm calling it:

$capxsum = cer_capxsum($mID);

When I plug the sql directly into my SQL Management Studio, it fires fine. But when I do this:

echo $capxsum["capxtotal"];

I get nothing...

What am I missing? Why does the sql fire, why do I get my sum but not be able to echo it?

Thoughts?