Complaints have prompted mobile phone game developer Gameloft to reduce the cost of playing My Little Pony: Friendship is Magic.
The "freemium" game is free to play or gamers can pay to progress faster. But some players say it can take years to finish without spending cash.
Campaigners worry about the number of such freemium games aimed at children.
But Gameloft said the complaints were from older users known as "bronies", not from children or their parents.
A "brony" is the term used to describe the adult fans of the My Little Pony game and of the TV show of the same title.
The game can be downloaded free from Apple's App store or the Android equivalent, Google Play.
It involves building and managing the town of Ponyville. Despite being free, players have the option to pay to progress faster, using the game's premium currency, gems.
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