From the Settings>Accounting page, click the "Add accounting integration" button as shown here:

Next, click “Connect,” sign into your QBO account, and follow the prompts.

When your QBO is successfully integrated, you will see it on the Accounting page:

If syncing is OFF, you'll need to manually enable it by following these steps:

By taking the steps mentioned above, you will be all set for syncing, whether that's our daily automatic syncing, or manually syncing Purchase Orders and invoices.