Full Slate will automatically sync your payment transactions entered via Checkout each time you save a transaction. You can immediately open your QuickBooks Online account and see the transaction there.
If you change something in QuickBooks Online that you want to see reflected in Full Slate (e.g. added or modified a client record, added or modified a sales tax rate, or updated your chart of account), you’ll need to go to Setup > QuickBooks Sync and click the ‘Synchronize now’ button to reflect the changes in Full Slate. You may also need to refresh your Full Slate browser.
The transaction sync is one-way from Full Slate to QuickBooks Online, so transactions recorded or modified in QuickBooks Online cannot be synced to Full Slate.