You'll have to contact directly our Developer Support so someone can help and fully address your concern about application integration. I'm here to help you accomplish this.
- Go to Intuit Developer Support.
- Select QuickBooks Online.
- Hit Ask a Question.
- Click Sign In.
But please know that you'll have to create a developer account first if you haven't created one. To do so, simply click the Create Account button on the Log in page.
If there's anything else that I can help you with, please let me know in the comment section down below. I'll be always around ready to help.