The REST API spec only alows for returning a single server so name the

endpoint appropriately.

synapse/rest/voip.py

@@ -24,7 +24,7 @@ import base64
 
 
 class VoipRestServlet(RestServlet):
-    PATTERN = client_path_pattern("/voip/turnServers$")
+    PATTERN = client_path_pattern("/voip/turnServer$")
 
     @defer.inlineCallbacks
     def on_GET(self, request):

webclient/components/matrix/matrix-service.js

@@ -765,7 +765,7 @@ angular.module('matrixService', [])
         },
 
         getTurnServer: function() {
-            return doRequest("GET", "/voip/turnServers");
+            return doRequest("GET", "/voip/turnServer");
         }
 
     };