This Alert indicates that a table in your application has almost reached its storage limit size. In order to keep the "quick" in QuickBase, tables have a maximum size limit. When this limit is reached, users are prevented from adding new records.
To see how close you are, you can check your application's
Use a field of type "Formula - URL (Link)". Set the cover text to "Click Here.." and then use a formula to point to a report that selects for only one record based on the Record ID# field which is unique for every record.
The URL for a report using the API is for example:
Instead of using Lastname: to search, use Email:, as some users do not have the Last Name and First Name values set for their user profile. Using Email: A-F returns the most inclusive list and will sum to the same number as presented in your account usage stats section.