It seems agreed that "curve" is best translated to منحنى, so there is nothing to debate here.

It is "payout" that I would like to address.

If you look around the internet for any mention of "payout" in an Arabic page, you will find that it is mostly used in the sense of dividend payout: the percentage of earnings that a company pays out to shareholders at the end of the year or the quarter. Of course, not all companies pay dividends, but in Arab countries, stock investing seems to focus more on dividends than on stock price growth as a return on investment, so the concept of dividend payout is very commonly discussed in Arabic websites dealing with stock investment. Since the payout in that context is a percentage of earnings, it is usually referred to as نسـبة دفع الأرباح. Here is an example:

https://books.google.com/books?id=t-9fDwAAQBAJ&pg=PA13&lpg=P...

The concept we have in your context is very different. It has nothing to do with stocks or dividends. Here the term refers to money paid out to sales people as a reward or an incentive. It is commonly known as "sales commission" or "bonus."

In their simplest form, sales commissions are known everywhere, because selling requires a personal effort that seems to increase and produce greater sales results when rewarded. In that simple framework, it is commonly referred to as مكافأة (often dubbed مكافأة تشجيعية and is considered to be equivalent to "reward") or عمولة (considered to be equivalent to "commission") or زيادة (usually considered to be equivalent to "bonus"). Here is an example for the use of مكافأة:

https://www.google.com/books/edition/Uṣūl_al_lqtiṣād/QRsEAAA...

And here is an example of مكافأة تشجيعية:

https://www.google.com/books/edition/أساسيات_وتطبيقات_التر/X...

And here is an example of عمولة:

https://www.google.com/books/edition/التأسيس_لمشروعات_تجار/h...

And here is an example of the use of زيادة:

https://www.google.com/books/edition/استراتيجيات_ادارة_الم/E...

These concepts and terms are commonly used, and there is not much debate around them.

The difficulty in your context is that it deals with a highly sophisticated scheme for calculating the amount of such commissions, bonuses, rewards, incentives, or whatever one could call them. The scheme envisioned here is so complex that it requires a highly sophisticated mathematical formula, one that can be described as a curve, hence the expression "payout curve."

This is why the expression has no standard Arabic translation. In Arab societies, rewarding a salesperson (or any worker, for that matter) is a far simpler affair. Amounts are often decided arbitrarily by the boss and is typically thought of as a sign of the company's generosity towards the worker.

In the West, especially in the United States, such incentives are thought of as hormones to milk as much output as possible, or like bait to attract the most productive workers. There is, therefore, a race for the most effective incentive scheme. Most of these schemes originate out of research by students in MBA programs and then find their way to real-life application. This is why these schemes are so highly mathematized, complete with formulas and graphs. These graphs are what they call curves. In Arab countries, such schemes are not popular. Therefore, there is no standard translation for "payout curve." Any suggestion you receive here is essentially just that: a suggestion.

Apart from whether the rewards are called "commissions" or "bonuses" or anything else, in the end there is a payout to be given to the salesperson. It is this word, "payout" that I want to address.

The only reason I would prefer المدفوعات (or المدفوع if you prefer the singular form) rather than الدفع is that the word الدفع strikes me as denoting the act of paying, while "payout" refers to the amount being paid. That is why I prefer المدفوعات and that is why I suggest منحنى المدفوعات as a translation for "payout curve."

I think any of the other suggestions presented here by my colleagues would be fine to use. I just thought perhaps might add just a little improvement.