service/BTCpayserver.md

@@ -254,6 +254,23 @@ delete the data, and restart:
     rm -r /var/lib/docker/volumes/generated_nbxplorer_datadir/_data/Main
     docker-compose -f $BTCPAY_DOCKER_COMPOSE start nbxplorer
 
+### Incorrect certificate
+
+If you try to connect to <https://btcpayserver.torproject.org/> and
+get a self-signed cert, that is because it's not the right
+server. Connect to <https://btcpay.torproject.org/> instead.
+
+If you connected to the right name and *still* get the wrong
+certificate, try to see if the Let's Encrypt companion is misbehaving,
+see:
+
+    docker-compose -f $BTCPAY_DOCKER_COMPOSE logs -f --tail=10 letsencrypt-nginx-proxy-companion
+
+Normal output looks like:
+
+    letsencrypt-nginx-proxy-companion    | Creating/renewal btcpay.torproject.org certificates... (btcpay.torproject.org btcpayserver-02.torproject.org)
+    letsencrypt-nginx-proxy-companion    | 2022-12-20 02:00:40,463:INFO:simp_le:1546: Certificates already exist and renewal is not necessary, exiting with status code 1.
+
 ## Disaster recovery
 
 In theory, it should be possible to rebuild this service from scratch