May I ask for new questions related to something else other than the original topic, to make a new topic for this in the future? 
Your code has a little mistake:
{% if custom.meerwaarde.soort == 'vrijwillig' %}
Meerwaarde afzonderlijk belastbaar tegen 16,5% en op te nemen in code 1603/2603 van de aangifte PB.
{% endif}
should be :
{% if custom.meerwaarde.soort == 'vrijwillig' %}
Meerwaarde afzonderlijk belastbaar tegen 16,5% en op te nemen in code 1603/2603 van de aangifte PB.
{% endif %}
Your {% endif %} was written down wrong.
Major TIP 
If you create code, you can always type if and then immediately TAB; you’ll see that the editor in Silverfin automatically creates your code (so no chances on writing down wrong code 
)