Decoupling from the western financial system and having a higher level of resilience from sanctions. You never know if the US will decide tomorrow you're not behaving as expected under the internal rules-based order.
Countries don't buy oil (or anything else) with a suitcase or few stuffed with $100 bills.* Instead, they have a really big bank move US dollars through the international banking system electronically.
Any really big bank that wants to keep its US-issued "Allowed to Handle US Dollars Electronically" License has got to follow a bunch of US-made rules. Which rules doubtless permit the US to make & enforce a very long blacklist, of various countries / organizations / people who the US doesn't want banks to work with.
(That said, I see no reason to suspect that Ghana has any interest in "Decoupling from the western financial system", as elzbardico put it. Though obviously the subjects of oil, gold, dollars, etc. are pushing a whole lotta people's emotional buttons in this item.)
*Yes, there are exceptions - usually involving sanctions-busting by folks who don't care about drawing hostile attention from the US.
Source?
There is no US-issued license required to use dollars internationally. This is stupid.
Do you mean this in some metaphysical sense? Because you can exchange USD for gods or services outside the US without the US government getting involved.