Plex unable to link up with Box

I have issue linking Plex with my Box account. I searched on google and both need to be paid accounts, which they are. However I still get error on Plex page saying that Box does not support direct links. Which is not true because I shared my files with other people and my Box account is fully paid for.

I am getting this error with the free account can some please respond where the setting is to be fixed or if it needs to be a paid account and even when its paid how to resolve.

Thanks