Hi vcharlottema-yah,
Is the receipt you're trying to reconcile showing and downloaded in the Bank transactions tab of QuickBooks Online? If yes, you can use the resolve difference option to allocate GST amount.
I recommend also checking in with our Customer Care Team. That way, one of our agents can check your transactions together and help you reconcile the receipts.
Check this link to learn more about: Reconcile an account in QuickBooks Online.
Post again in the Community if you have further questions about QuickBooks Online.