We have a button on the opportunity object that is a part of the Octive managed package and is submitting the proposal for an approval when clicked. We would like to customize it so that when the opportunity is at stage 'Closed or Lost'
or 'Closed or Won'
and user clicks the button they get an error message.
The button URL is as following:
/apex/tinderbox__create_document?sObjectType=Opportunity&recordId={!Opportunity.Id}