Inconsistent dollar-shekel exchange rate

I would appreciate a little more elaboration because I simply don't understand the halakhic logic.
I'm intentionally exaggerating the question
If he can set any rate he wants
Sometimes he can set two percent and sometimes three percent on the amount I owe him, he's actually earning interest on the amount.
What don't I understand here?

Questioner, following these and other questions you asked in the thread about my question, I understand that you don't know at all what the prohibition of interest is. Instead of asking a lot of specific questions, I think you should take a brief look at the laws of interest. All (!) of the questions you asked are very far from interest.

Regardless, if he's actually stealing from you, maybe there's a blind man here. A question for Rabbi Michi.

Indeed. I see that you are very busy with this. I suggest that you study the laws of interest in an orderly manner.

David S.

I may not have the same knowledge, experience, and Torah understanding as you do when it comes to interest laws.
After studying the halacha on the subject, I found myself even more confused. As someone who is involved in business, I try to move forward and be more careful to observe the halacha better and more accurately than before.
My question stems from reading the following article:
https://www.dirshu.co.il/%D7%94%D7%90%D7%9D-%D7%94%D7%99%D7%AA%D7%A8-%D7%A2%D7%99%D7%A1%D7%A7%D7%90-%D7%9E%D7%95%D7%A2%D7%99%D7%9C-%D7%AA%D7%9E%D7%9 9%D7%93-%D7%95%D7%9B%D7%99%D7%A6%D7%93-%D7%9E%D7%95%D7%AA%D7%A8-%D7%9C%D7%94/?srsltid=AfmBOoqLKiNLhppWA2M2xf04Ef8TxFUtAqxkihQyw2tg9tPX6mQ-LKtm

After reading the article, I wondered whether a payment against another currency is considered interest, especially when the business owner is the one who determines the exchange rate.
If you have knowledge of these laws, I would appreciate it if you could explain why this situation is not considered interest.
Thank you very much!

I don't mean to be a complainer. I'm really saying that you should at least learn the basic laws of interest. It's very (very) clear why interest is involved in the article in the ’Darshu’ and not in your questions. Don't read articles about interest, read a summary of a few paragraphs about the principles of interest, that will be enough.
I understand very little about the laws of interest, but there is a little that I remember for you:
The three basic conditions for interest are 1. Loan 2. Addition to the principal 3. Pre-condition of the addition.
From here it gets more complicated, a common red flag is “withholding fee” – If you were paid for withholding your money, suddenly your money looks like a loan.
Basically, if you don't have all three or something similar, you don't have a case to argue at all. (Even if there is no 3, it is considered “usury dust” and is forbidden by the Rabbis, but here it gets complicated, I think… I am not an expert myself)
The Rabbis also have ‘late usury’ ‘early usury’ and ’usury of things’… In short, there is something to learn. But all your questions are not at all about a loan or anything similar to a loan or a gift of some kind.