@Sam Boyer there's no way to make custom field required, and the trigger "when a user doesn't fill out a custom field" doesn't really make sense (since, until someone fills out a custom field, they haven't filled it out by definition :)
Do you mean something like if someone hasn't filled in a particular field and then attempts to move the card to the next list or something like that?
Perhaps you would be better off using something like Google Forms for the data collection and then populating the fields in Trello when a form response is received
If you had to thrive a new habit during a lockdown, what would it be? Trello
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