I have implemented Paypal subscription with a seven-day free trial, then the payment is captured if the user did not cancel his subscription. which webhook event is fired in the normal case (payment done after trial period)?
All Subscription payments will result in the event PAYMENT.SALE.COMPLETED
the moment the transaction completes.
Other than BILLING.SUBSCRIPTION.ACTIVATED
for the case of trials starting without a payment, you can build all subscription logic based on listening for just PAYMENT.SALE.COMPLETED
and making a note of when you expect the next one. Other billing subscription events aren't necessary nor useful to track.