Walmart is offering free gift cards to Alabama customers after accidentally overcharging them on tax. 

The retail chain made the mistake on Sept. 1 after a new law lowered the state's tax on groceries from 4% to 3%. 

Attempting to adjust their systems to the new rate, Walmart accidentally charged customers both the old tax rate and the new tax rate at the same time. The same mistake was made at the company's Sam's Club locations.

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The company is now offering gift cards to anyone who was overcharged during the period of malfunction. 

The $5 Walmart gift cards will be issued to customers who bring their Sept. 1 receipt showing they were overcharged to customer service at any location. 

Sam's Club members in Alabama are being offered a similar opportunity, but the big box retailer will be giving out $5 in Sam's Cash on their store account instead of gift cards. 

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The gift cards and store credit are only being offered until Sept. 18.

Walmart is the nation's largest retail chain and has over 144 locations in Alabama.

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Walmart is partnering with Alphabet Inc.'s Wing to expand drone delivery to 60,000 additional homes in Texas. 

The service with Wing, an on-demand drone delivery provider powered by Alphabet, will be offered from two stores in the Dallas metro area over the coming months, Walmart said Thursday. 

In utilizing drones, Walmart says it's able to provide on-demand delivery for customers living within an approximate six-mile range of Walmart stores that offer the service.

Fox Business's Daniella Genovese contributed to this report.