When there is limited or no space left in your OneDrive you will notice that OneNote or Class Notebook may stop working correctly, in addition your files may stop syncing.

 - OneDrive account nearly full -

If you see this Symbol, your ‘OneDrive’ account is nearly full and you will be required to delete or move files. The Trust allocates 10GB of space per person, Files such as Videos should always be saved in SharePoint and not in your ‘OneDrive’.
 - OneDrive account full -

If your OneDrive is full you have used up all allocated space available. You will need to delete files or move them elsewhere.
Once you have deleted files no longer needed, we recommend checking your Downloads folder to ensure there is nothing needed in there and once you have deleted those files, you can then go to the recycle bin, and also the second stage recycle bin and empty them which will then recover some space for you, as shown below.