This is the percentage charged every time you borrow USDP. All issuance fees collected will go to developing the project. For example, if the issuance fee is 0.9% and you want to get 10 USDP, you'll have to issue (10 / 0.9991) USDP. 10 USDP will go to you, and the remaining amount will go to the development fund.