Workflow Rule Assignment

Hi,

I stuck in workflow rule assignment.

Scenario-

I Created customize workflow for FI Park & Post with 3 decisions (Post, Reject, Review) but in decision i want to assign multiple SAP Users. For that i created one table which is having Initiator Users with their approvers and after that created function module which i used in Rule to get user from table and it is working in simulation.

The problem is when i am assigning the rule in User Decision step it is not triggering.

What is the proper step for rule creation and assignment?

Regards,

Varun