Global variable updates its value to the intended value but resets to the original value

Hi, I am trying to create a system where there is Aura, and an Aura converter. There's an Aura counter at the top of your screen and you can convert a certain item to Aura points. However, when I try to get that certain item by 'withdrawing' it, it should deduct a value from the global variable which in this case is the Aura points. However, it does work but it resets back to the original value. Any help?