Fix callback key expression example.
MODIFY
versions/3.0.2.md
versions/3.0.2.md
@@ -1883,7 +1883,7 @@ $method | POST
$request.path.eventType | myevent
$request.query.queryUrl | http://clientdomain.com/stillrunning
$request.header.content-Type | application/json
-$request.body#/failedUrl | http://clientdomain.com/stillrunning
+$request.body#/failedUrl | http://clientdomain.com/failed
$request.body#/successUrls/2 | http://clientdomain.com/medium
$response.header.Location | http://example.org/subscription/1

Fix callback key expression example.