From 8ce60865178b46f0d420dde5c5bc373cc17a22da Mon Sep 17 00:00:00 2001
From: "nicolas.dorier" <nicolas.dorier@gmail.com>
Date: Tue, 2 Jun 2020 11:46:04 +0900
Subject: [PATCH] Add Backward compatibility section

---
 bip-xxxx.mediawiki | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/bip-xxxx.mediawiki b/bip-xxxx.mediawiki
index be5ed260..c9d2d085 100644
--- a/bip-xxxx.mediawiki
+++ b/bip-xxxx.mediawiki
@@ -346,6 +346,12 @@ With payjoin, the maximum amount of money that can be lost is equal to two payme
 * [[https://github.com/JoinMarket-Org/joinmarket-clientserver|Join Market]] is in the process of implementing the protocol.
 * [[https://github.com/bitcoinjs/payjoin-client|JavaScript sender implementation]].
 
+==Backward compatibility==
+
+The receivers are advertising payjoin capabilities through [[https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki|BIP21's URI Scheme]].
+
+Senders not supporting payjoin will just ignore the `pj` variable and thus, will proceed to normal payment.
+
 ==Special thanks==
 
 Special thanks to Kukks for developing the initial support to BTCPay Server, to junderw, AdamISZ, lukechilds, ncoelho, nopara73, lontivero, yahiheb for all the feedback we received since our first implementation.