my app was suddenly got rejected with following reason:
Guidelines 3.1.1 - In-App Purchase and 3.1.3(c) - Enterprise Services
We noticed in our review that your app offers enterprise services that are sold directly to organizations or groups of employees or students. However, these same services are also available to be sold to single users, consumers, or for family use without using in-app purchase.
When an organization or group buys access to your app's enterprise services, you don't need to use in-app purchase. But when providing access to an individual user, consumer, or for family use, you should use in-app purchase.
Next Steps
Here are two ways to resolve this issue:
You can revise your app to only provide your services directly to organizations and groups of employees and students.
Otherwise, you can revise your app to give App Store customers the option to purchase these services with in-app purchases.
Resources
Learn more about our policies for apps that offer enterprise services in App Store Review Guideline 3.1.3(c).
Learn more about implementing in-app purchase in your app.