You should add a result tag in the template so you can reference to it from somewhere else, like this:
| {% t “Conclusie op basis van professional judgement” %} | |
|-------------------75%-------------------------|----20%-----|---------+
| {% t "Continuïteit is " %} {% input custom.detail.bedreigd as:select options:“bedreigd|niet bedreigd” %}.| |{% if custom.detail.bedreigd != blank %} {% assign ind = 0 %} {% else %} {% assign ind = 1 %} {% endif %} {% unexplained ind as:indicator %}
| {% input custom.letter.Commentaar as:text size:mini %} | |
{% result "bedreigd" custom.detail.bedreigd.updated_at %}
So this part was missing from your code:
{% result "bedreigd" custom.detail.bedreigd.updated_at %}
More info for result tags can be found here:
PS registers can only be used to take in values, so this code:
{{ $30+custom.detail.bedreigd.updated_at }}
can never work as well.