Hello

Can anybody tell me how can I earn bitcoin from this site
https://www.ipayyou.io/

They have Earn Bitcoin option on this site.
I want to know how it works.

They have earning calculator on this site.

According to my calculation :-
If I purchase $100 of gift card from amazon, then
I have to sell in $75 to them.

Where is the earning?

or do you have any other site to earn like this?