Can’t join Facebook group as page I want

I tried to join a group as my business page. Our business manages a few facebook pages for our clients (over 20). When I tried to switch to our page from my personal profile. It only gave me one option, one of our client’s pages. I tried another group and the same thing, same page. Anybody know why this is? I’ve searched quite a bit on google with no results other than a similar post to this forum. Thanks