ipad won't download assignments off my online student portal.

Hi, I'm in school currently. I have a notability app on my tablet which i use to take notes for school. I have also been downloading lecture slides, and articles and uploading them into my notability app. within this past week the download button is not working anymore. I click on it and nothing happens. I checked my tablets storage and I'm only using 1/3rd of the available storage.