Mr Green, owned by William Hill, has been ordered to pay £3m ($3.8m) to the National Strategy to Reduce Gambling Harms, as part of the Gambling Commission’s investigation into online casinos.
The company has been penalised for failing to implement effective procedures to prevent harm and money laundering, and has also had to pay costs of £10,349 to the Gambling Commission.
Mr Green has committed to conducting a compliance assessment of an additional 130 customers.
The failures came before William Hill acquired the company in 2019. The statement from the Gambling Commission references issues regarding what the operator accepted as evidence of adequate source of funds, as well as not carrying out social responsibility interaction with a customer who won £50,000.
William Hill previously confirmed in its financial presentation for 2019 it had set aside £3m in the likelihood of the penalty being issued.
Richard Watson, Gambling Commission Executive Director, said: "Our investigation uncovered systemic failings in respect of both Mr Green’s social responsibility and AML controls, which affected a significant number of customers across its online casinos.
"Consumers in Britain have the right to know there are checks and balances in place which will help keep them safe and ensure gambling is crime-free."