International sales, currency exchange, coupons

HI,

I see several issues with the description of your problem so I'm not able to understand what is your problem.
Could you first help me understand the issue ?
1.If you have the products price only in EUR and that the system converts from EUR to BPS in order to see the prices in BPS, I guess you use the BPS currency rate that you can edit when you edit the BPS currency via the menu System>Currencies.
I don't see the link here with the fact that the discounted price is fix ? If you configured a discount for the product via the menu Orders>Discounts, the price of the product won't change daily regardless of how you configured your discount.
So that sentence is not clear "The customer will not accept daily changes of the BPS to the Euro so the discounted price is fix."

2. Coupons are discounts of the type "coupon" in HikaShop. Coupons apply to all the cart once you enter the code of the coupon on the checkout. Coupons do not change the price of products since they apply on the checkout for the whole cart and the list price of products is thus not affected by coupons so I also don't understand what you mean by "We add ad coupon reducing the price from the list price."

Could you maybe provide an example of what you want to achieve ? Like:
user A can buy product X which costs Y euros for him
user B can buy product X which costs Z pounds for him
user A can't see the price Y of product X and vice-versa
(it's just an example and I'm not sure if it fits what you want).
Also, if you have a coupon/discount, it would be great to have a screenshot of the options of the coupon/discount to make sure that we understand how you configured it.

The biggest problem is see here is that user B should see the price in pounds and not the other users because there is no option to restrict currencies based on the user or the user group of the user.
If that's really needed, then all I can think off is to develop a HikaShop plugin and view overrides to display the price like you want on the listings, the product page and the cart.

Without any customization, you can get this by having discounts restricted to user B and user C:
user A can buy product X which costs 1 euros per minute for him
user B can buy product X which costs Y euros per minute for him
User C can buy product X which costs 0,70 euros per minute for him
user A can't see the price of user B and C of product X
All user shall see the price of product X which cost 1 euros per minute
And if you want users to be able to purchase in pounds in that case, you can activate the HikaShop currency switcher module.
Having a fixed rate of conversion between EUR and GBP is easy. Just set the rate that you want in the GBP currency and make sure that the hikashop currency rates auto update plugin is turned off.