Success! I helped this business getone of their Facebook pages under their business portfolio. They had been trying to do this for months and it seemed like they had done everything.
I thought I may not be able to do it because what could I try they haven't? But I did it.
This might lead to a bit more work back in the musical instrument wholesale industry. Working in a space you care about really makes a difference
The business portfolio id is used as part of the URL for Facebook Business Centre, so I replaced the id for a business centre I had access to with the problem business portfolio. Fortunately they still had access to that business portfolio and could accept the request to disconnect that page from the old portfolio, opening it up to joining a new one.
This only worked because they had access. We would still be stuck if it was controlled by someone else