When you receive this error, it's likely due to having too many custom fields.
QuickBooks Time has a limit of six custom fields, two of which will be needed for Task Type and Role. For successful integration, there must be two free custom fields, otherwise, the integration attempt will produce an error of "Too many custom fields in QBT".
Please remove all but four of your custom fields in QuickBooks Time and try syncing again. Here are the steps to remove the extra custom fields:
Steps to Edit Custom Fields:
Go to Feature Add-ons, then select Custom Fields.
Select the field you want to edit.
To archive an item: In the Edit Field window, select the three gray dots, then Archive item. If you'd like to archive multiple items, check the box to the left of each item and select Archive.
After all changes are made, select Save.
If you're still experiencing issues, please reach out to the Support Team at firstname.lastname@example.org.