Symptoms
You see the following message when signed in to Office.com:
Out of space. Your OneDrive is out of storage space and changes can't be saved. To free up space, delete files you don't need then empty the recycle bin.
Cause
You have exceeded your OneDrive for Business quota.
Resolution
Delete or remove any unnecessary files from OneDrive for Business.
TIP: Certain file types (such as video) take up more space than pictures or text documents.
OUTCOME
You will no longer receive the message.