Cannot create Webhooks ("FeatureFlagService is not defined")

[Mario]

DevTools in Chrome print out

ReferenceError: FeatureFlagService is not defined
at s.render (batch.js:9:7179)
at selectionChanged (batch.js:9:12089)
at s.trigger (batch.js:3:1093)
at s.change (batch.js:3:4474)
at set (batch.js:3:2734)
at select (batch.js:9:2177)
at s.<anonymous> (batch.js:9:13710)
at s.trigger (batch.js:3:1093)
at s._onModelEvent (batch.js:3:9179)
at s.trigger (batch.js:3:1181)