Why does my post say 'Uncategorized' on the calendar?

When you add a post to your calendar directly, you will see it's listed as 'Uncategorized'. This is because the post was not added to a group in Post Groups. Post Groups is where you organize all your posts into groups.

In the example below, the post on Wed 6th Jan is listed as 'Uncategorized' as it was added to the calendar directly. The post on Thu 6th Jan is listed as 'Nutrition' as it's a post that was shared from the Nutrition group created in Post Groups.