The quick answer: merchants decide the Annual Growth Rate (AGR) and any other rewards and offers they give to you.
The details: The merchant is solely responsible for its offers and rewards. They are also solely responsible for the goods and services they provide to you and for honouring the advance payments you make to them by allowing you to buy goods and services from their participating outlets in accordance with their offer terms.
You can see the merchant’s terms and conditions in the Explore section of the app. You need to agree to these each time you make an advance payment to them. You should check them every time as they may have changed.
This creates a separate contract between you and the merchant, and any merchant AGR or other reward referred to in the offer will only apply to that advance payment. HyperJar is not a party to that contract.