I can share some information and help you get pointed in the right direction regarding integrating Qwilr with QuickBooks Online.
For third-party applications to help with the integration of online stores and QuickBooks Online, check out our Intuit Solutions Marketplace at https://apps.intuit.com/ or, you can visit our Apps page through your QuickBooks Online account. You can find tons of apps that are compatible and designed to work with QuickBooks Online.
Also, there's a community dedicated to developers and utilizing applications with QuickBooks. I recommend that you sign up and post this question to our separate online forum called Intuit Developer Community.
You can also reach out to Qwilr, they can provide more details on how to their application work with QuickBooks.
I'll be around to help you further if there's anything else you need with QuickBooks integrations.