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This can happen because of the restrictions QuickBooks Online has placed on its character usage. The QuickBooks Online Customer API states: the DisplayName, Title, GivenName, MiddleName, FamilyName, Suffix, and PrintOnCheckName attributes must not contain colon (:), tab (\t), or newline (\n) characters. There are other sync rules associated with BQE CORE-QuickBooks Online integration.
This issue can also occur if the related client/customer records are not properly mapped between BQE CORE and QuickBooks Online. If you are syncing project phases or working with parent project hierarchies, ensure that the parent client in CORE is linked to the corresponding customer in QuickBooks Online.
In BQE CORE, projects sync to QuickBooks Online as sub-customers rather than QuickBooks Online Projects. However, when importing data from QuickBooks Online into CORE, both QuickBooks Online projects and sub-customers are imported as projects in CORE. Check CORE Help Center for details.