Jatinder Singh, 39, in May 2021 placed a $100 deposit in his then-partner Thevamangari Manivel's account on cryptocurrency website Crypto.com.
He was notified that his investment would be refunded because of a discrepancy in account names.
But in what County Court Judge Martine Marich described as a significant accounting mistake, the staff member issuing the refund typed a bank account number into the funds box - transferring more than $10.4 million into Manivel's bank account.
Singh told his partner to transfer the large sum of cash from her Commonwealth Bank account to their shared bank account before the transaction could be reversed.
Singh was on Tuesday sentenced to three years in prison over the theft of $6 million spent in a flurry of 160 transactions over 10 months.
Manivel made two separate transfers of $2 million to a bank account in Malaysia.
When the cryptocurrency platform realised the mistake - seven months later during an audit - it and the Commonwealth Bank attempted to contact the pair to recover the money.
The pair ignored the companies' repeated attempts, believing it was a scam.
By that time, they had already gone on a spending spree, including buying two properties and gifting $1 million to a friend.
Singh was arrested and charged with theft in March 2022 when he told police in an interview he believed the money came from "winning something" on the Crypto.com website.
Judge Marich, in her sentencing remarks, noted Singh's cognitive challenges, including an "extremely low" IQ, which reduced his ability to foresee the impacts of his actions.
"Cognitive challenges and challenges in navigating social rules weigh more heavily on you than it would for others," she said.
A difficult stint on remand also exacerbated his deteriorating mental health including anxiety and depressive symptoms and suicide ideation.
The impact of media coverage of his crimes left him feeling scared to leave his house, fearing his reputation would be harmed by the charge, Judge Marich told the court.
"(You were afraid) of others in the community gossiping about you and your parents finding out," she said.
The judge described Singh's actions as "entirely situationally motivated" offending and he had very good prospects of rehabilitation.
"You have not reoffended since being granted bail, a lack of priors and a pro-social lifestyle aside from this offending leads me to conclude that you present with a low risk of reoffending," she said.
The Indian national has already served 361 days in prison.
Singh's former partner and co-accused Manivel was jailed for 209 days in 2023 after she was arrested attempting to board a flight to Malaysia with a one-way ticket.
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