While a regular sale generally does not have any Ribbis issue, whenever a customer prepays for something that the seller does not have readily available in-stock, a Ribbis issue applies. The payment is a loan, and the item is repayment of the loan. If prices go up the repayment is more than the loan, creating a Ribbis problem.

In order to avoid any Ribbis problem the merchant would need to have the items in stock, or it can be something that's available with a set price on the market.

Being that some Mishloach Manos items might not be put together at the time of sale (it is more than a month before Purim) this problem can arise.

A Heter Iska makes the transaction an investment and not a loan. This takes care of all Ribbis issues. We at Pretzel Plate are the company you are investing with, and our profits will be paid in the form of Mishloach Manos.