when should one use 支払い or 支払

Question

In lots of contracts I see the word 支払. When should one use 支払 instead of 支払い?

Answer 1

"支払" and "支払い" are almost same in the meaning and interchangeable with each other. When to use them is also a very controversial issue even for Japanese and me. From my understanding, "支払" is used mainly in official and commercial use including contracts and "支払い" is used in other cases.