Thomson Reuters
A customer counts his cash at the checkout lane of a Walmart store in the Porter Ranch section of Los Angeles
Customers can snag the money by using the app's Savings Catcher tool, which scans shoppers' receipts and compares the prices they paid at Wal-Mart to the prices advertised for the same items elsewhere.
If the app finds a lower advertised price, then Wal-Mart will issue a gift card in the amount of the difference.
The tool is wildly popular.
When Savings Catcher launched nationally in August of 2014, users of Wal-Mart's app spiked from 4 million users to 14 million in a single month, reports Shelly Banjo at Quartz.
Now it's the third most successful
The app is likely so popular because of how often users get money back.
Wal-Mart executives said in February that about half of the receipts that the app had processed until that point had qualified for a refund because it found lower prices at different stores.
"The psychological benefit is huge," Banjo writes. "Now, instead of checking other retailer's prices every week, shoppers get in the habit of visiting the Walmart app after each trip to see how much money they saved."
Users can take advantage of the tool in three ways.
They can either scan the code at the bottom of their printed store receipts using the scanner in the Savings Catcher section of the Wal-Mart app, or enter their receipt number into the app.
Shoppers can also enter their receipt number into the Savings Catcher website.
The tool will scan all the items they purchased and compare the prices to those found in print and online versions of weekly ads for top retailers in their area.
Shoppers can submit up to seven receipts a week.