We added the following to the QWeb invoice report and have it working:

<tr>
                            <td>Payments</td>
                            <td class="text-right">
                                <span t-esc="o.amount_total - o.residual" t-esc-options="{&quot;widget&quot;: &quot;monetary&quot;, &quot;display_currency&quot;: &quot;o.currency_id&quot;}"/>
                            </td>
                        </tr>
                        
                        <tr class="border-black">
                            <td><Strong>Balance Owing After Installation</Strong></td>
                            <td class="text-right">
                                <span t-field="o.residual" t-field-options="{&quot;widget&quot;: &quot;monetary&quot;, &quot;display_currency&quot;: &quot;o.currency_id&quot;}"/>
                            </td>
                        </tr>