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Before even going over extending the visa, there's another problem. The penalty for overstaying is, since October 1, 2017, 1 million rupiah per day, instead of 300K previously. That's 75 USD per day. This is of course non-negotiable. For a few days there are no other consequences. Beyond that, all bets are off.
As a Nigerian, he had to apply for a so-called "Calling Visa": the Immigration Office in Jakarta has to approve the visit, not just the embassy. Whether he had a business visa or a tourist visa should be easy to determine: the process is not the same, and the type will be written on the sticker.
Whether it can be extended or not will be also mentioned. But in any case, it has to be done before expiry. After that, it's fine country...
Now, Indonesia being what it is, there may be a visa agent with a cousin or six at the Immigration office. While many if not most agents are out there to make easy money, there could be a few who could really help. But bottom line, overstaying could be an expensive proposition in Indonesia.
Note that after 60 days, there won't be a fine to pay (although Immigration will try their best to make you pay), just deportation and blacklisting...