There are many potential sources of error during synchronization, from wrong mapping configurations to missing user rights to PHP errors in user functions. When a synchronization is launched from the BE module a status is displayed when the operation is finished.
The extension tries to report at best on the success or failure of the operation. Turning on the “debug” mode (see the Configuration chapter) will provide additional information.
As described in the Configuration chapter, it is also possible to receive a detailed report by email. It will contain a general summary of what happened during synchronization, but also all error messages logged by the TYPO3 Core Engine, if any.