How to force pop-up to add a comment when an issue transitions to On Hold

[Samantha Sharkov]

Hello!

Trying  to create an automation rule where every time an issue transitions On Hold a window dialogue to add a mandatory comment would open. 

[Mikael Sandberg]

You can't do this with automation, since they execute after the issue is transitioned. What you should do is add a transition screen in the workflow and make the comment field required by adding a validation rule to that transition.