Walmart is bringing back an app that lets shoppers skip the checkout line and pay for items themselves on their smartphones.

It first tested a version of the app, called Scan & Go, in 2013. But the giant retailer discontinued it after customers said it was confusing to use. Walmart said Wednesday that it learned from the initial test and redesigned the app to make it easier to use.

A test of the updated Scan & Go app began this year at some stores in Houston, Orlando, Florida and near Walmart’s headquarters in Bentonville, Arkansas. The test is now being expanded to stores in Dallas and Nashville, Tennessee.

The company declined to say exactly how many stores are taking part in the test.

With the app, shoppers scan items with their phone as they shop. When they’re done, they can pay for the items through the same app. Customers have to show their phones to employees on their way out to prove that they paid.

Walmart said the app has been available at all of its Sam’s Club warehouse stores since October.