Hey @adarsh_anncode,
Are you uninstalling and reinstalling in the same billing cycle? The reason I ask is that would be expected. From our docs:
When an app is uninstalled, Shopify automatically cancels the subscription. A credit isn’t applied to cover the cost of the rest of the billing period. Merchants can reinstall and use the app for the remainder of the billing period.
What Dylan suggests should work to check if the current subscription is active or cancelled and then request billing. Alternatively, to simplify the process, you could just force the billing page on all installations and use the AppSubscriptionReplacementBehavior to determine how to replace the current charge.
Let me know if any of that will work.