Why aren't all customers syncing over to QuickBooks?

If the customer list in QuickBooks is shorter than the customer list in Acctivate, it is because the QuickBooks customer list only shows the new customers with invoices.

To have the customer list in QuickBooks match the customer list in Acctivate, you can go into Configuration Manager> Customer > Customer Options. Under Synchronization,  you can uncheck the box next to 'Only synchronize new customers with invoices'.

After saving this change and performing a QuickBooks sync, the customer list should be updated to match on both QuickBooks and Acctivate.