Cent marketplace, which sold an NFT of Jack Dorsey's first tweet for $2.9 million, has stopped most of its NFT transactions because a number of people were selling tokens of content that did not belong to this.

2021 has seen sales of NFTs (non-fungible tokens) skyrocket to $25 billion. NFTs are supposed to record the ownership of a digital file, and anyone can mint them, which explains why reports of counterfeits have become commonplace.

Cent, which is based in the USA, sold the former Twitter CEO's tweet as an NFT last March and stopped allowing the trade of NFTs as of February 6, CEO Cameron Hejazi told Reuters.

Hejazi called this a "fundamental problem" in the NFT market.

"There's a spectrum of activity that is happening that basically shouldn't be happening - like, legally," Hejazi said.

The buying and selling of NFTs of tweets are still active on the marketplace, but all other sales have been suspended.

Hejazi said that there are three main problems in the marketplace: people selling unauthorized copies of other NFTs, people making NFT content that doesn't belong to them, and people selling sets of NFTs that resemble a security.

"It kept happening. We would ban offending accounts but it was like we're playing a game of whack-a-mole... Every time we would ban one, another one would come up, or three more would come up."

Cent, which has 150,000 users and revenue "in the millions", is a relatively small NFT platform, and Hejazi said the issue of fake content is one that is rampant in the industry.