Islam slave trade

[Athene]

All the slaves sold to Europeans on the West African coast were the prisoners of Africans.

Untrue.
Europeans (primarily the Portuguese, British, and Dutch) did conduct slave raids along the West African coast; Especially in the early phases of the of the TST.

In regards to the captives who were sold to slavers by African middlemen--Africans did not subscribe to  the notion of a homogeneous "African" or "Black" ethnicity--No reason why they would considering the sheer amount of ethnicity/genetic diversity among people living on the continent. That's a box Eurocentrists invented and tossed them all of them in.

Worth noting, when running with the "they sold themselves" narrative. For the most part, leaders and merchants were selling and trading captives/POWs they regarded as foreign; Not subjects of their own tribes/kingdoms.