@CBroeders It worked for me as well now!
I have used the Modern template for this. These are the steps I took:
1. Clone modern.html to child theme
2. Add this piece of code (use your own custom property)
{
"column_title": template_translations.tax_pluimen.message,
"column_property": "tax_pluimen"
},
3. Clone the line_item_table module to child theme
4. Add the second piece of code. I edited the format_date to format_number as my custom property was a number and not a date property
{% elif item.column_property == 'tax_pluimen' %}
<td class="{{ cell_print_max_width_class }}">
{{ property_value|format_number(LOCALE) }}
</td>
5. Add the custom property to the Select Column Property on the right side (when still in the cloned line_item_table)
6. You can now add the custom property in your HubSpot quote
7. This did some things to my styling, which I have fixed with CSS