+ /// The id returned by [`ChannelManager::send_payment`] and used with
+ /// [`ChannelManager::retry_payment`].
+ ///
+ /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
+ /// [`ChannelManager::retry_payment`]: crate::ln::channelmanager::ChannelManager::retry_payment
+ payment_id: Option<PaymentId>,