This was such a long drag, but I have found the solution.
Long story short, he had to remove the page from his business account for it to become "unclaimed" after which I claimed it with the actual business account.
You will click "settings" tab at the top right of the screen of the page. Ensure you have "general" tab selected on the left hand side. You will then look for "Visitor Posts" section. It should be the second from the top. You will click edit on the right. Then choose required option.
Depending on your Page's category, different features are available for your Page. The table below outlines the different Page categories (across) and the features that are available to them (down):