Jose Manuel Jurado Diaz does some sleuthing:
In this blog article, we will delve into a common error encountered when synchronizing data with Azure SQL DataSync. We’ll explore the error message “Error #1: SqlException Error Code: -2146232060 – SqlError Number: 515, Message: Cannot insert the value NULL into column ‘ID’, table ‘dbo.Customers’; column does not allow nulls. INSERT fails. SqlError Number: 3621, Message: The statement has been terminated.” We will provide a detailed explanation of the error and its possible causes, followed by a T-SQL code snippet that reproduces the error scenario.
Click through for four possible causes.