Someone offered to post a few "relevant" ads in his Facebook business page and he agreed.
He received an email from Facebook with a link to the "Facebook Business Manager". He clicked and agree to share the page with the other person.
[I guess he clicked more "I agree" buttons than what he says. I have zero proof, but users click in whatever button appears in the screen without reading.]
The other person got administrative privilege of the page, and removed him. So he was locked out of his own business page.
The other used posted a lot of spam in the page. IIRC he says the links are scammy. I'm not sure, but I'd better not try.
He tried to contact Facebook, but the support didn't solve the problem. In particular because it was the business page, not the personal page.
[Some time after this video, the problem was solved.]