Hi @Mrudul_T! This is by design - subscription contracts follow an ownership model where only the app that created the contract can query it or receive webhooks for it.
I tested this on a dev store and confirmed that webhooks fired for contracts my app created, but contracts from Shopify Subscriptions aren’t even visible when querying subscriptionContracts. Same limitation applies to webhook delivery.
This was confirmed as expected behavior in a similar thread. The only partial workaround is orders/create with selling_plan_allocation in line items, but that only captures initial purchases and not renewals or cancellations.