It is possible to make API calls and create custom apps with a free account (Individual), but could you please answer the following questions?
Hi 
Hope you’re well! To address:
Free Accounts:
have limited access to Box’s API and developer tools can create and integrate basic custom apps, but may have limitations on how these apps interact with Box services or the complexity of the apps you can develop Paid Accounts: offer more extensive API access with higher limits on API calls and additional functionality which is crucial for developing more complex and high-traffic custom applications access to advanced Box features such as Box Platform API (and Enterprise Features often have better support for integrating with third-party applications and services. This can include more options for single sign-on (SSO), enterprise-level security protocols, and custom workflows higher performance and greater storage capacitiesPlease visit our pricing page regarding API calls for paid accounts. This page will also provide you an overview and side by side comparison of our plans and features.
Feel free to contact our Sales Team to discuss more about features and if you’re interested in upgrading.
Have a great day ahead! 
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.