Volto: Action To Get Data From RestApi Doesn't work

I created a restapi for a Plone addon some weeks ago. The code is here:

I tried to get the categories from this restapi (as a first step), but I wasn't successful yet. I tried to follow (adapted) the Plone 6 training documentation for this (chapter 47). I created:

I tried to get with console.debug inside the categories.jsx (inside components/Categories), if the construct is working. I got only:
{ loaded: false, loading: false, error: null }
as result.
I looked into categories.js from reducers and found out that I most likely only got the 'initialState' and nothing.
Thus in my opinion the connection to the restapi is not established yet.
Any hints how to proceed?

Some things you can do to debug the problem:

  • inspect the network trafic in your browser developer console. Is the backend server responding properly? Is the endpoint really called?
  • Install and peruse the Redux DevTools to observe the redux actions and the how they mutate the global state
  • Start volto with DEBUG=superagent yarn start, it will log all network trafic on the nodejs server
  • path: ${url}/@projectcategories may or may not be weird, depending on the way you do the setup. Usually paths are "fixed" before passing them to actions, using either getBaseUrl or flattenToAppURL.

I started yarn with the debug option and got the following, if I call in Volto a project URL with '/projectcategories':
GET http://[IP]:3000/++api++/templates/test-45/@projectcategories -> 200 +17ms
superagent GET http://[IP:3000/++api++/templates/test-45/@projectcategories/@workflow -> 404 +20ms
superagent GET http://[IP]:3000/++api++/templates/test-45/@projectcategories/@navigation?expand.navigation.depth=1 -> 404

Thus there is no content to fetch at that URL, right?

The restapi endpoint in the Plone backend for this is:

And if I call this endpoint with Postman I get e.g. the JSON content:

Thus the endpoint seemed to work, but I can't get connected to it within Volto.

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