Permits
What are you looking for, ad hoc or block permits, traffic rights etc. there is a heck of a lot of difference. Luanda to Nairobi, who's gonna pay the enroute charges etc. There is a basic standard format and protocol, no free form, simple you pose the question, and you supply the answer, they grant the permission.
Operator XXX ABC Airlines
Requests Overflight and/or landing permission for
the following operation/s
Flight Number/s AO001etc
Make it easy to read and in the simple (request) question and (response)
answer. You are asking and are giving the answer the folks at the other end are gonna ask.
Always specify the scheduled FIR/published territorial boundary enter/exit points/times.
Be honest about your cargo! "general" can be assumed to be 7.62mm stuff.