subtotal field in my client area invoices page not showing any data

hi,

I need to display subtotal in my client area invoices page and I've added the subtotal field to my template. (see snippet of my client area invoice template below)

However, when i log in any client, no data gets populated to the subtotal field.

can someone advise me on how to fix this?

thanks


<form method="post" action="clientarea.php?action=masspay">
<table class="table table-striped table-framed table-centered">
<thead>
<tr>
<th{if $orderby eq "id"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=id">{ $LANG.invoicestitle}</a></th>
<th{if $orderby eq "date"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=date" >{$LANG.invoicesdatecreated}</a></th>
<th{if $orderby eq "duedate"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=dueda te">{$LANG.invoicesdatedue}</a></th>
<th{if $orderby eq "Sub Total"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=Sub Total">{$LANG.invoicessubtotal}</a></th>
<th{if $orderby eq "total"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=total ">{$LANG.invoicestotal}</a></th>
<th{if $orderby eq "status"} class="headerSort{$sort}"{/if}><a href="clientarea.php?action=invoices&orderby=statu s">{$LANG.invoicesstatus}</a></th>
<th>&nbsp;</th>
</tr>
</thead>
<tbody>
{foreach from=$invoices item=invoice}
<tr>
<td><a href="viewinvoice.php?id={$invoice.id}" target="_blank"><strong>{$invoice.invoicenum}</strong></a></td>
<td>{$invoice.datecreated}</td>
<td>{$invoice.datedue}</td>
<td>{$invoice.sub total}</td>
<td>{$invoice.total}</td>
<td><span class="label {$invoice.rawstatus}">{$invoice.statustext}</span></td>
<td class="textcenter"><a href="viewinvoice.php?id={$invoice.id}" target="_blank" class="btn">{$LANG.invoicesview}</a></td>
</tr>