Rxjs reducing to make serially http calls

observables.js

// https://stackblitz.com/edit/rxjs-map-pipe-study-b2qoje
import { of, from } from 'rxjs'; 
import { map, flatMap, catchError } from 'rxjs/operators';

console.clear();

function fakeApiCall(value) {
  console.log('Calling', value)
  var lookupValues = { "a": 123, "b": 234, "c": 345, "d": 456 };
  throw new Error('Hmmmm we are breaking things!')
	// return { id: value, lookup: lookupValues[value] };
}

const totesToBeCreated = ['0014745', '0022'];

const sourceTotes = of(totesToBeCreated);

const example = sourceTotes.pipe(
  flatMap((totesArray) => {
    console.log('arr', totesArray);
    return totesArray.reduce((previousObservable, toteNumber) => {
      console.log('tote', toteNumber);
      return previousObservable.pipe(
        flatMap(response => {
          console.log('response', response)
          return of(fakeApiCall(toteNumber))
        })
      )
    }, of(null))
  }),
  catchError((error) => {
    console.log('Something went wrong!', error.message);
  })
)
  
const subscribe = example.subscribe();