And another thing I didn't mention is that there are already currencies common across several independent states, the Central African franc and the West African franc, which are in all effects actually the same currency. These are used across former French colonies. Originally, they were pegged to the French franc, and from there they inherited a peg to the Euro. There are talks to convert this to a new currency called the Eco, which would also include different non-francophone West African countries.

However, even that remains an illusion according to many economists. The launching of this new currency has been postponed several times since the beginning of the 21st century, Especially countries like Nigeria are dragging their feet on this.

https://www.dw.com/en/west-africas-eco-currency-plan-remains-a-pipe-dream/a-58136111