When reconciling in QuickBooks, you have to make sure the bank statement data matches with the transactions in QuickBooks Online.
If you're unable to reconcile, make sure all entries are entered into the program. If there are missing deposits that is in the bank statement but not in QuickBooks, create them using the + New button on the toolbar.
Once added, make sure to categorize the transactions properly. These steps will guide you how to match a QuickBooks entry to online banking:
Go to the Banking menu and select the transaction to expand the view.
Find the payment from the bank and choose Find match. See this sample snapshot:
Review the entries in the Match transactions page. These transactions are those that were already added in QuickBooks.