All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Having asked the Division of Financial Affairs at the General Command of the Jordan Armed Forces, it was made clear to us (Iftaa` Department) that the sum paid upon getting promoted to Senior Warrant Officer is the total of the contributions paid by that person over the years of serving as Warrant Officer. This is in addition to the rewards that he/she had deserved during that period. Moreover, rewards are calculated based on years of service and not as an interest for the value of that sum.
In conclusion, there is nothing wrong with taking the reward referred to in the above question. We ask Allah to save us and all Muslims from unlawful money. And Allah the Almighty knows best.