f fix pay_pubkey_with_id docs missing change

Author: TheBlueMatt

lightning-invoice/src/payment.rs

@@ -477,12 +477,14 @@ where
 			.map(|()| payment_id)
 	}
 
-	/// Pays `pubkey` an amount using the hash of the given preimage, caching it for later use in
-	/// case a retry is needed.
+	/// Pays `pubkey` an amount using the hash of the given preimage and a custom idempotency key,
+	/// caching the invoice for later use in case a retry is needed.
 	///
-	/// The hash of the [`PaymentPreimage`] is used as the [`PaymentId`], which ensures idempotency
-	/// as long as the payment is still pending. Once the payment completes or fails, you must
-	/// ensure that a second payment with the same [`PaymentPreimage`] is never sent.
+	/// Note that idempotency is only guaranteed as long as the payment is still pending. Once the
+	/// payment completes or fails, no idempotency guarantees are made.
+	///
+	/// You should ensure that the [`PaymentPreimage`] is unique and the corresponding
+	/// [`PaymentHash`] has never been paid before.
 	pub fn pay_pubkey_with_id(
 		&self, pubkey: PublicKey, payment_preimage: PaymentPreimage, payment_id: PaymentId,
 		amount_msats: u64, final_cltv_expiry_delta: u32