How to dispatch two actions in one epic, which could be in the same or in another reducer - redux-observable

Question

I have two ducks (ui and backend) with epics in them.
I need to trigger two actions after finishing backend operations
One of these actions reside in the backend duck, the other in the ui duck.
I started with the background action and things worked as expected.
Adding the second action leads me to issues, as I can reach the action (console logs correctly), but not the reducer (no log)
The challenge I'm trying to solve is:
Kicking off two actions in one epic
dispatching an action in another reducer
My code looks similar to this:
the backendDuck's epic:
fetchFooEpic : (action$, store) =>
action$.pipe(
operators.filter(action => action.type === types.LOAD),
// start added section for second call
operators.switchMap(action => {
const response = operators.from(fetchSomeUrl(action))
.pipe(
operators.of(uiDuck.actions.fetchUserFulfilled(response.props)),
),
operators.catchError(err => {
console.error('Error happened!', err.message)
return rxjs.of({ type: types.ADD_CATEGORY_ERROR, payload: err })
})
return response
}),
// start added section for second call
// original first call
operators.map(a => ({ type: types.ENDACTION, payload: a.payload })),
operators.catchError(err => {
console.error('Error happened!', err.message)
return rxjs.of({ type: types.ADD_CATEGORY_ERROR, payload: err })
})
)
the uiDuck:
export actions={
...
fetchUserFulfilled: (value) => {
console.log('hello from action')
return ({ type: types.FETCHUSERFULFILLED, payload: value })
},
...
}
...
export default function reducer(state = initialState, action) {
switch (action.type) {
case types.FETCHUSERFULFILLED:
console.log('hello from reducer')
return {
...state,
user: action.payload,
}
...

Answer 1

Turns out I was combining the two calls in the wrong way.
For being able to pipe along, the piped observable needs to return an observable again.
When mapping to another redux-action, it seems to me that it doesn't return an observable (?) thus, the call needs to happen for all desired redux-actions at the same location (eg with concat)
For the sake of completeness I strive to explain all parts of the code in comments
import * as operators from 'rxjs'
fetchFooEpic : (action$, store) =>
action$.pipe(
operators.filter(action => action.type === types.LOAD), // Filter
operators.switchMap(action => // restart inner actions on each call
operators.from(fetchSomeUrl(action)) // creating observable from result
.pipe( // starting new flow on observable (self)
//operators.tap(a => console.log('Now running fetchfooepic 2', a)), // dedicated location for sideeffects
operators.switchMap( // restart inner actions on each call
(response) => operators.concat( // Kicking off several actions sequentially (merge() would do that in parallel)
operators.of(uiDuck.actions.fetchUserFulfilled(response)), // addressing the redux action in other reducer
operators.of(({ // addressing the redux action via the type in this duck (ENDACTION is controlled by epics only, no action exists for it)
type: types.ENDACTION,
payload: response
}})),
)),
operators.catchError(err =>{
console.error('Shit happens!', err.message) // errorhandling
return rxjs.of({ type: types.ADD_CATEGORY_ERROR, payload: err })
})
)
)
),
Generally the functions are documented with some (more or less understandable) examples in
https://rxjs.dev/api/index/function/