After you have clicked Redeem Offer, followed the redemption steps and purchased the item, simply return to Rebaid. On the top of homepage you will see a box where you should enter your order number, then click Submit. I have attached a screenshot for reference.
After you submit your order number your redemption is confirmed and your rebate payment is scheduled. There is nothing else you need to do to receive your rebate. As soon as your rebate check is mailed you'll receive a payment notification and your rebate check will arrive a few days thereafter.