The integration between Housecall Pro and QuickBooks online will only affect new invoices after initial setup. So invoices that were in Housecall prior to QuickBooks integration will not be automatically pushed over.
In a situation where an invoice needs to be manually pushed to QuickBooks, you’ll want to go to the job details page (i.e. open the invoice), and scroll to the card that says QuickBooks Online (This will be found under the Activity Feed at the bottom of the invoice).
Once there, you’ll click the three dots in the top right-hand corner of the card and select Push invoice/payment to QBO from the drop-down. Your invoice and any payments on the invoice will then push to your QBO account, and a link will appear to each on this card. You can click the link to be redirected to the invoice or payment in your QBO account.