Here are some of the common considerations for import validation.
Importing Invoices requires Invoice Ref and Invoice Date
If you have a Billed amount to import against a time sheet, then you need a value in the spreadsheet for a Bill Ref and Invoice Date.
Job does not exist
Make sure you add the job and re-import. The import data may have the wrong job short name.
The Bill Totals exceed the time entry totals
You cannot over bill time, so the totals of the bills cannot exceed the time. Filter the import spreadshee to work out which bill allocations based on the TE Ref. In the import you can see which bills are assigned ot the time entry based on the Bill Ref.
Job type provided does not match
The job type specified in the import spreadsheet doesn't match the job or job type history. Make sure the job types are from the available you
The import file is missing headers
The import file is not the correct format. Download the file template.
Divide by zero
This will be caused by having zero hours.