Business Process Flow steps mandatory issue

Hi All,

I am working MS CRM 2015. I want change mandatory field on BPF step to not mandatory. This should be done when BPF step changed. Please refer following screenshot

Scenario :: When I mark complete to "Introduction Company" field on BPF, I need to change "Proposed Solution" field as not mandatory, Currently by default it is mandatory field. To implement this functionality i used "Business Rules" and JavaScript but not worked. Below is the sample i used.

JavaScript:: 

Xrm.Page.getControl("header_process_proposedsolution").setRequiredLevel("none");

Business Rule::

kindly let me know am i missing anything or suggest any solution.