Introduce RetryableSendFailure::InvalidAmount

Some upcoming changes require a new `PaymentFailure` variant to handle cases where a
Bolt11 invoice specifies an invalid amount. This commit introduces the variant,
setting the stage for its usage in subsequent commits.

Author: shaavan

lightning/src/events/mod.rs

@@ -598,6 +598,10 @@ pub enum PaymentFailureReason {
 	///
 	/// [`HeldHtlcAvailable`]: crate::onion_message::async_payments::HeldHtlcAvailable
 	BlindedPathCreationFailed,
+	/// Incorrect amount was provided to ChannelManager::pay_for_bolt11_invoice.
+	/// This happens when an amount is specified when Bolt11Invoice already contains
+	/// an amount, or vice versa.
+	InvalidAmount,
 }
 
 impl_writeable_tlv_based_enum_upgradable!(PaymentFailureReason,
@@ -610,6 +614,7 @@ impl_writeable_tlv_based_enum_upgradable!(PaymentFailureReason,
 	(6, PaymentExpired) => {},
 	(7, BlindedPathCreationFailed) => {},
 	(8, RouteNotFound) => {},
+	(9, InvalidAmount) => {},
 	(10, UnexpectedError) => {},
 );
 
@@ -1702,7 +1707,9 @@ impl Writeable for Event {
 					Some(PaymentFailureReason::InvoiceRequestRejected) =>
 						&Some(PaymentFailureReason::RecipientRejected),
 					Some(PaymentFailureReason::BlindedPathCreationFailed) =>
-						&Some(PaymentFailureReason::RouteNotFound)
+						&Some(PaymentFailureReason::RouteNotFound),
+					Some(PaymentFailureReason::InvalidAmount) =>
+						&Some(PaymentFailureReason::InvalidAmount)
 				};
 				write_tlv_fields!(writer, {
 					(0, payment_id, required),

lightning/src/ln/outbound_payment.rs

@@ -500,6 +500,10 @@ pub enum RetryableSendFailure {
 	///
 	/// [`BlindedPaymentPath`]: crate::blinded_path::payment::BlindedPaymentPath
 	OnionPacketSizeExceeded,
+	/// Incorrect amount was provided to ChannelManager::pay_for_bolt11_invoice.
+	/// This happens when an amount is specified when Bolt11Invoice already contains
+	/// an amount, or vice versa.
+	InvalidAmount,
 }
 
 /// If a payment fails to send to a route, it can be in one of several states. This enum is returned
@@ -958,6 +962,7 @@ impl OutboundPayments {
 					RetryableSendFailure::RouteNotFound => PaymentFailureReason::RouteNotFound,
 					RetryableSendFailure::DuplicatePayment => PaymentFailureReason::UnexpectedError,
 					RetryableSendFailure::OnionPacketSizeExceeded => PaymentFailureReason::UnexpectedError,
+					RetryableSendFailure::InvalidAmount => PaymentFailureReason::InvalidAmount,
 				};
 				self.abandon_payment(payment_id, reason, pending_events);
 				return Err(Bolt12PaymentError::SendingFailed(e));