def client_max_amount_reverse_swap(self) -> Optional[int]:
        """Returns None if swap is not possible"""
        provider_max = self.get_provider_max_forward_amount()
        max_ln_send = int(self.lnworker.num_sats_can_send())
        max_swap_size = min(max_ln_send, provider_max)
        if max_swap_size < self.get_min_amount():
            return None
        return max_swap_size
Returns None if swap is not possible
electrum/submarine_swaps.py