We are always aiming to make our customers feel valued, nithin@pixelscri.

I appreciate the time and effort you've spent in posting your concern on Intuit Developer page.

I can see your urgency to have an answer to your issue. However, there may be a large volume of posts to the developer's department that delays their response. 

In the meantime, let's wait for their reply so you'll get an answer in integrating QB API with your mobile application. They can also further assist you to obtain an access token to acquire authorization.

Meanwhile, I'll be adding this great Community resource in case you've got other QuickBooks concerns such as setting up payments, managing your income and expenses, running reports, etc. Please refer to this article for more details: Community help articles.

Keep me posted if you have other questions about managing your QuickBooks account. I'll be happy to help. Stay safe!