matrix: proxy calls to '/_synapse/client'

services/matrix.nix

@@ -78,13 +78,21 @@ in
         forceSSL = true;
         useACMEHost = "${domain}";
 
-        # Or do a redirect instead of the 404, or whatever is appropriate for you.
-        # But do not put a Matrix Web client here! See the Element web section below.
-        locations."/".return = "404";
-
-        locations."/_matrix" = {
+        locations =
+          let
+            proxyToClientPort = {
               proxyPass = "http://[::1]:${toString clientPort.private}";
             };
+          in
+          {
+            # Or do a redirect instead of the 404, or whatever is appropriate
+            # for you. But do not put a Matrix Web client here! See the
+            # Element web section below.
+            "/".return = "404";
+
+            "/_matrix" = proxyToClientPort;
+            "/_synapse/client" = proxyToClientPort;
+          };
 
         listen = [
           { addr = "0.0.0.0"; port = clientPort.public; ssl = true; }