JFNotes

I am trying to add a notebook that my buddy has added me to and I keep getting the error "Couldn't join notebook, Notebook join limit reached." We have tried removing me and and re-adding me to the notebook several times but it still won't let me join the notebook. My understanding is that the EN notebook limit is 250, so I'm not sure why I am unable to join the notebook. I searched the forum but couldn't find anything about this particular error. Does anybody have any advice for me regarding this issue? I have attached a picture of the error. I also get the "Notebook cannot be retrieved, Unable to join notebook" error message when attempting to Add Notebook on the iOS app.