That’s revisionism.This link explains the depth of Benin's involvement in the slave trade and also explains some of the confusion that causes people to interpret it as some major player in the trade.
Granted Benin didn’t sell its own people (other kingdoms & empires also didn’t sell their own people apart from Igbos who were sold by their fellow Aros & Dahomey until Gezo outlawed it) - it doesn’t negate the fact that it sold other people.
Benin was a powerful empire that was also very wealthy. Where do you think it got the bulk of its enormous wealth from? Palm Oil trading which became the source of wealth for West African kingdoms towards the end of the 19th century wasn’t even a thing then. You can argue that the numbers being thrown out there by Europeans is bogus since they did more capturing with superior weapons than buying. But saying Benin didn’t sell slaves is a lie.
Perhaps when I have time I’ll post journals from the explorers that were present at the time.
Chattel slavery was a normal thing across the world at that time - no need to deny it. But the heinous crimes committed during transatlantic & trans-saharan slavery weren’t normal & that’s a stain on humanity.