Amazon has been forced to refund up to $70 million for in-app purchases made by kids. It comes after the retail giant dropped its appeal against last year's ruling that found Amazon guilty of not doing enough to warn parents that free apps could contain paid upgrades.

The case first appeared in court in 2014, and in April last year, a district court found that Amazon billed customers for unauthorized in-app purchases incurred by children using apps and games that were downloaded from its Appstore. The court ruled that Amazon failed to obtain parental consent for the purchases made by children.

Around $70 million in charges made between November 2011 and May 2016 could be eligible for a refund. The FTC says that details on the refund program, which will be carried out by Amazon, will be announced "shortly."

"This case demonstrates what should be a bedrock principle for all companies — you must get customers' consent before you charge them," said Thomas B. Pahl, acting director of the FTC's Bureau of Consumer Protection. "Consumers affected by Amazon's practices can now be compensated for charges they didn't expect or authorize."

Amazon requested to refund the purchases in the form of gift cards last November, but this was rejected by a U.S. district judge. The company will be expected to issue money back to credit and debit cards, or send out paper checks.