Hi Lai124.
Being about to use a software developer kit to create your own applications is always welcome with QuickBooks Desktop. I'd be happy to point you in the right direction to get this message resolved.
Making sure your sales tax feature is properly turned on would be the first step here. I suggest following the steps in this article to guarantee they are.
If your taxes are turned on and you're still getting an error mentioning that they are not then I'd recommend reaching out to the developer of the kit to find out what's going on. As this would not be an issue with QuickBooks itself.
If you have any questions let us know and we'd be happy to help!
