Quickbooks migration failed unexpectedly for several reasons. One common reason is that the migration process was not completed correctly. This could include not connecting to the correct server, incorrect data input, or not mapping the data correctly. Another issue could be caused by incompatibilities between the versions of Quickbooks being used. If the versions are too different, the migration may fail. Additionally, Quickbooks migration can fail due to technical issues such as a slow or unreliable internet connection or a server error. To ensure a successful migration, it is important to double-check all data input, ensure proper mapping, and ensure that the versions being used are compatible.