fix challenge URL computation

lib/AccountManager/App.pm

@@ -591,7 +591,7 @@ sub req_complete_challenge {
             '%s&action=complete_challenge&federation=%s&entity=%s&email=%s',
             $self->{configuration}->{app}->{url},
             $self->{in}->{federation},
-            $self->{in}->{entity},
+            $self->{in}->{entityid},
             $self->{in}->{email},
         ),
         lh        => $self->{lh},