Companies such as car manufactures give customers rebates as a way of convincing the customers to buy their products. Here's how rebates usually work. You buy the product. Then you send the manufacture a document that is called a proof of purchase within X days of your purchase and the manufacture mails you a check for X amount of money.
@riojpita The rebate request is a document (or it can be done online). The rebate itself is money (or a check or other document with monetary value). If the original actually said that rebates must be mailed within 3 days of purchase, that would mean that the company offering the rebate must mail the rebate within 3 days of purchase. This makes no sense. Normally, the rebate request is sent first from the purchaser to the company, then the rebate is sent from the company to the purchaser.
@MetRon Thank you M. It was in this passage. “We received your mail-in rebate card this week. Unfortunately we will not be able to honor it because the rebate offer had already expired when you mailed it. Rebates must be mailed within three days of purchase”