fixed websocket preview bug

fixed websocket preview bug, because of interface changes:

__Tasks:__

- [x] gather feedback for my changes
- [x] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | no => don´t know why(=
| Fixed tickets | none
| Doc           | none