To participate in the McDonald's Customer Satisfaction Survey via www.mcdvoice.com, visit the official site within 7 days of your purchase. As written on mcdtalks.com , Select your preferred language—English or Español—to begin. You’ll need a valid 26-digit survey code printed on your McDonald’s purchase receipt, often accompanied by BOGO sandwich offers (Buy One, Get One Free). If your receipt doesn’t have a survey code, you can still enter other required transaction details to access the survey. Once completed, a unique survey validation code will be generated, which you can redeem for the promotional offer listed on your receipt. Mcdtalks Mentions that current promotional offer is “buy 1 get 1 sandwich” This system helps McDonald’s collect customer feedback and continuously improve service at participating restaurant locations.