You may see this warning message if you have recently upgraded from a trial license to a paid plan and are the owner of more than one organization.
The organization you have upgraded to a paid plan will not have any issues. Any other organizations you own will revert to the 2 collaborator plan at the expiry of the trial period. The warning message you see when you access Planbox is related to these other organizations. The message will disappear at the end of trial period.
The way Planbox works is that you are essentially paying a subscription for X collaborators in one organization. Just make sure all your collaboration occurs and projects are created/managed in the upgraded organization that is on a paid plan and you can ignore the warning message.