Gimme a quick idea for what to do in my project

I basically want a structure and languages required to do my project given below. I want to make a store that contains discord login(I did that already) Now my the customer will do some tasks and get some "coins" added in their accounts and claim them for items. Now I want to design how the coins will be added subtracted without any bugs to ensure safe process Am not asking for the code but just the structure and languages to use