Gus Palmer/BBCOnlyFans creator Rebecca was subjected to abusive messages and violenceWarning: contains details of violence that some readers might find distressingRebecca, an OnlyFans creator, joined an agency after they promised to help her earn more on the adult social media platform - instead, they abused her, threatened her daughter and dispatched violent masked men to attack her at home, she says."They were lovely at the beginning." The 29-year-old from south Wales says her new managers told her she was beautiful and they had "never seen a girl" like her before. But within weeks they turned "quite controlling", insulting her appearance and forbidding her from going out with her friends, she tells BBC Three documentary OnlyFans: Inside the Machine.The abusive behaviour escalated after she changed her account login details, worried the agency - which could access her account - would lock her out, she says."I will have you and your daughter wrote off," said one message seen by the BBC.A brick smashed her window and, a few weeks later, two masked men arrived at her house. One came inside, she says, strangled her and threw her "up and down the stairs". She shows the BBC photos of bruises over her legs and throat.Her ordeal forms part of a pattern of allegations against agents, self-styled online as OnlyFans managers (OFMs). They promise to help creators grow their businesses on the platform but, BBC findings show, are sometimes exploitative and threatening.We heard from 60 UK OnlyFans creators and embedded ourselves in one of the largest private Telegram groups for agents, called OFM Empire, which has 24,000 members. There, we found advice on signing creators, taking control of their accounts and reaping profits - often using the threat of violence. One user called this the "pimp method".OnlyFans has known about concerns about over-exploitative OFMs for at least four years, when allegations about agencies first surfaced in the international press.But, for the first time, our investigation focuses on the UK, where OnlyFans is based. It shows the platform is not doing enough to protect creators from exploitation, according to the human rights experts and lawyers who have seen our findings."What Rebecca experienced are all recognised signs of exploitation - control, coercion, financial pressure and an inability to leave freely," the UK's independent anti-slavery commissioner, Eleanor Lyons, tells the BBC. "It is something that the government needs to look at in more detail… we potentially have a platform which is enabling exploitation, enabling abuse."An OnlyFans spokesperson said: "The allegation we 'turn a blind eye' [to these issues] is unfounded."The company takes user safety "incredibly seriously" and invests "heavily" in measures to protect its community, the spokesperson continued, adding that it meets all its duties under the Online Safety Act."OnlyFans' relationship is with our creators and fans and we are not connected with, and do not endorse, any third parties including management agencies. "Unfortunately, we cannot review or influence any contractual relationships creators choose to enter into outside the platform as we are not party to them."Gia Clarke and Lily Phillips are both successful OnlyFans creators but say women on the platform can be vulnerableMore than 4.6 million OnlyFans creators worldwide upload videos and photos for their paying subscribers. The platform takes a 20% cut. One of the UK's social media success stories, the company that operates OnlyFans, Fenix International Limited, reported annual pre-tax profits of $684m (£513m) in its latest filing.A global ecosystem of OFMs has grown alongside the platform, chasing the success. They promise to attract more subscribers and boost earnings - and, in exchange, OFMs take a proportion of the creators' pre-tax earnings, commonly 50%.Gia Clarke, a UK creator who has been posting on OnlyFans since its launch 10 years ago, says she receives more messages from OFMs than from fans. "The concept [of OFMs] is really good, it's just that there are too many unqualified people... because there are no regulations, the models don't know who to trust," she says, describing some OFMs as "predatory".Creators' OFM contracts shared with the BBC show managers taking up to 70% of earnings. Many demand full access to account logins and impose fines on creators who try to leave contracts early."They [OFMs] are taking advantage... which is almost placing these content creators in servitude to the agents and agencies, trapped in a contract which is unfair," says Matt Jury of human rights specialist law firm, McCue Jury & Partners.Sophie Kemp, head of public law at Kingsley Napley, agrees: "This isn't really a fair contract situation at all. They seem to be the first step in the road to exploiting creators."