Log in to your Checkbook.io account.
Go to "Settings" on the bottom left-hand side of the page.
When in Settings, click on the "Profile Info" tab.
When in Profile Info, look for the "Integrations" section.
In the Integrations section, press the "Connect to QuickBooks" under the Quickbooks logo.
You should then see a window that looks like the above. Press the "Connect" button in the bottom right. Proceed through the remaining process to finish connecting your checkbook account to quickbooks.