I have warned many times on this blog (especially here, here, here, here, here, here, here, and here – with examples from Ireland, the UK, Australia, New Zealand, and the US) that the recipient of a mistaken payment not only has a duty to make restitution of that unjust enrichment but also faces potential criminal liability for theft if the payment is kept (and, worse, spent) rather than returned. A recent cause célèbre from South Africa provides another cautionary tale:

Sibongile Mani sentenced to 5 years’ imprisonment for theft of NSFAS funds

Walter Sisulu University (WSU) student Sibongile Mani [left] has been sentenced to five years’ imprisonment for theft relating to R14 million [€870,000] accidentally credited to her account by the National Student Financial Aid Scheme (NSFAS) in 2017.

East London Regional Court Magistrate Twanette Olivier found Mani guilty of stealing R818,000 [€51,000] of the funds.

She was only entitled to a R1,400 [€87] food allowance and was accused of failing to report when R14 million [€870,000] was credited to her account erroneously. She instead embarked on a spending spree. …

A little more background:

Key events that led up to the sentencing and appeal of NSFAS ‘millionaire’ Sibongile Mani

…
June 2017
A technical glitch led to funding administrative company Intellimali erroneously transferring R14m into Mani’s account.

It is believed that Mani spent R820 000 at 48 merchants in 73 days. She was meant to receive only her monthly R1 400 food allowance.

September 2017
Intelimali opens a theft case against Mani, saying that instead of reporting the error, she spent the money. …

The Court has given her leave to appeal.

Update: there’s more information here: Student splashed out on private jets, parties and designer clothes after being accidentally paid £850,000 food grant (15 Sept 2022)