www.wysiwygwebbuilder.com

I'd like to conditionally show a field based on the content of another field. I'm guessing I'll need something like:
{% if fielda == 'VISA' %}
show.textarea99
{% endif %}
But I'm not sure of the syntax / placement.

I cannot help you with programming related questions.

But maybe you can use 'Conditions' instead?
https://wysiwygwebbuilder.com/conditions.html