How to get Process Finish Button event in Dynamics CRM?

I am using Dynamics 365 online instance to integrate sales process. I have one condition where I need to change the Probability field value to 100 when user clicks on Finish button in Close Process Stage.

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I have done some research and found that (OnProcessStatusChange event) can help to get business process flow status change (statuses: Active, Finished, or Aborted)

Ref Link: OnProcessStatusChangeEvent

I have checked this by adding this to form OnLoad event like below, but nothing happens.;

Is there any other solution?