async def notify(self, address: str, URL: Optional[str]):
        """
        Watch an address. Every time the address changes, a http POST is sent to the URL.
        Call with an empty URL to stop watching an address.

        arg:str:address:Bitcoin address
        arg:str:URL:The callback URL
        """
        if not hasattr(self, "_notifier"):
            self._notifier = Notifier(self.network)
        if URL:
            await self._notifier.start_watching_addr(address, URL)
        else:
            await self._notifier.stop_watching_addr(address)
        return True

        Watch an address. Every time the address changes, a http POST is sent to the URL.
        Call with an empty URL to stop watching an address.

        arg:str:address:Bitcoin address
        arg:str:URL:The callback URL
        
electrum/commands.py