Kumi had long flaunted luxury items online to his more than 100,000 Instagram followers.
This raised suspicions about the sources of his income.
US prosecutors say victims were allegedly targeted through social media and online dating platforms, lured in via frequent and intimate conversations.
This would escalate to “requests for money or valuables under false pretences – such as urgent medical needs, travel expenses or investment opportunities”.
The monies, or valuables, were then directed to co-conspirators posing as third parties. Kumi allegedly distributed the money to his associates in the US and in Ghana.
Kumi, who is from the town of Swedru in southern Ghana, was arrested in a joint Ghana-US operation last year.
There is some disagreement about Kumi’s true age, with his lawyer saying he 28 years old and US prosecutors saying he is 31, external.
The case is being prosecuted under the US Elder Abuse Prevention and Prosecution law.
US authorities have in recent months stepped up their crackdown on criminal networks operating in the US and West Africa who seek to defraud elderly Americans.
Last week, extradited Ghanaian fraudster Joseph Kwadwo Badu Boateng – popularly known as Dada Joe Remix – pleaded guilty in the US, external to using romance and inheritance schemes to defraud Americans.
In December, a court in the US also sentenced Oluwaseun Adekoya, a Nigerian ringleader of nationwide bank fraud and money-laundering conspiracies, to 20 years in prison for laundering over $2m.
Additional reporting by Natasha Booty