It’s a scam. If you reply they will ask you for a credit card number or bank account number to pay for shipping and handling and insurance. They will spend all of the money in the account. They will never send you a gift card. If you visit the website in the message it will download spyware and viruses and heaven knows what else.
Delete the message. Do not reply to it. Do not visit the website in the message.
WalMart knows the scam is going on, but the scammers move often and can't be found.