Meta (formerly Facebook) reportedly charged its Internet users in developing countries like Pakistan, Indonesia and the Philippines, in the name of offering them free access to the Web.
Meta's Internet service, called Free Basics, is offered via Meta Connectivity (formerly Facebook Connectivity) and is supposed to provide users with "access to communication tools, health information, education resources and other low-bandwidth services" at no charge.
Launched in 2013, the initiative currently serves more than 300 million people globally.
According to a report in The Wall Street Journal, the users in Pakistan have been charged the most for using Facebook's "free" Internet at a total of $1.9 million, with nearly two dozen additional nations also affected.
According to the social network, the issue stemmed from a glitch in its software, which has now been fixed.
Facebook partners with mobile carriers in developing countries to give users free access to Facebook and some other websites.
"Internal company documents show that many of these people end up being charged in amounts that collectively add up to an estimated millions of dollars a month," the report mentioned.
Many of the users have inexpensive cell phone plans that cost just a few dollars a month, often prepaid, for phone service and a small amount of internet data.
They don't realise they've been getting charged for using mobile data until they run out of funds.
The issue appears to stem from Facebook's software and user interface (UI), with videos at the root of the problem.
Glitches in Meta software let some videos appear in the Free Basics programme, which let users pay for watching those videos.
Meta said it has fixed the problem.
"We tell people that viewing photos and videos will result in data charges when they sign up, and we do our best to remind people that viewing them may result in data charges," a Meta spokesperson told The Verge.
"The issue identified in the internal report that affected some of those reminders has largely been addressed. We'll continue to work with our partners to meet our obligations to these users and ensure accurate and transparent data charges."
The Free Basics programme is not available in India as in 2016, the Telecom Regulatory Authority of India (TRAI) had disallowed service providers from offering or charging discriminatory tariffs for data services purely on the basis of content.
Facebook later cut off free internet service for India, saying "Free Basics is no longer available to people in India".