Listen for incoming subscriptions

In this example, we will use the sub2 SDK to set up a listener for incoming subscriptions to our address. This is useful for anyone who wishes to accept payments with sub2 as you can validate that a subscription has successfully gone through. It is assumed that sub2-sdk is installed and set up as done here.

const unwatch: WatchEventReturnType = sub2SDK.watchIncomingSubscriptions(recipientAddress, callbackFn);

Here recipientAddress is of type `0x{string}` and callbackFn is of type (subscription: Subscription) => any. The callback function is defined by you and is what is called on newly observed subscriptions to the address. For example, you can make a callback function which checks that the subscription has the correct parameters and if so update your backend and register the user as subscribed.

The returned value unwatch of the viem type WatchEventReturnType is a function that can be called to stop listening for events.