If a payment fails to sync from MineralTree to QuickBooks Online due to the error "Account Period Closed" (you can find the error descriptions by running the "Payment Sync Failures" report from the REPORTS tab), this means that the Closing Date in QuickBooks Online is set to a date after the date(s) of the payments trying to sync.
To allow the payments to sync, you need to temporarily lift the Closing Date restriction in QuickBooks Online. To do this,
1 -- Go to * --> Account and Settings
2 -- On the next screen, choose "Advanced" on the left and then view the Closing Date under "Accounting". Note that payments with dates before the Closing Date will fail to sync from MineralTree to QuickBooks Online. To temporarily suspend the Closing Date function, simply uncheck the box next to "Close the books".
3 -- Reach out to Support to have the payments re-synced. After they've synced, you can check this box again.