Redeeming a free sandwich through the McDonalds survey is quick and easy. After making a purchase, keep your receipt and visit the www.mcdvoice.com survey website. Enter the required details from your receipt, such as the store number, date, and time of visit. Complete the survey honestly by sharing your dining experience. Once finished, youll receive a validation code on the screen. Write this code on your receipt and bring it with you on your next visit. Present it at the counter to redeem your free sandwich, subject to McDonalds terms and conditions.