Error: internal at new HttpsErrorImpl when invoking Firebase https callable cloud functions

This is the error I get whenever I call manageSubscription() which invokes the https callable cloud function:

core.js:4081 ERROR Error: internal
    at new HttpsErrorImpl (index.cjs.js:60)
    at _errorForResponse (index.cjs.js:155)
    at Service.<anonymous> (index.cjs.js:560)
    at step (tslib.es6.js:100)
    at Object.next (tslib.es6.js:81)
    at fulfilled (tslib.es6.js:71)
    at ZoneDelegate.invoke (zone-evergreen.js:364)
    at Object.onInvoke (core.js:27149)
    at ZoneDelegate.invoke (zone-evergreen.js:363)
    at Zone.run (zone-evergreen.js:123)

Using:

"@angular/core": "^10.0.4",
"@angular/fire": "^6.0.3",

Here is my Apps Module:

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    BrowserAnimationsModule,
    AngularFireModule.initializeApp(environment.firebaseConfig),
    AngularFireFunctionsModule,
    SharedComponentsModule,
    AppRoutingModule
  ],
  providers: [
    { provide: ORIGIN, useValue: 'http://localhost:5001' }
  ],
  bootstrap: [AppComponent]
})

I am invoking https callable cloud function in my Service:

Added dependency:

constructor(private firebaseFunctions: AngularFireFunctions) {}

This is the method:

public manageSubscription(){
  this.firebaseFunctions.useFunctionsEmulator('http://localhost:5001');

  const functionRef = this.firebaseFunctions.httpsCallable('testFunction');
  functionRef({ returnUrl: 'window.location.origin' })
    .subscribe(response => {
      console.log(response);
  });
}

This is the cloud function:

import * as functions from 'firebase-functions';
import * as admin from 'firebase-admin';

admin.initializeApp();

exports.testFunction = functions.https.onCall((data, context) => {
    console.log('reached');
  return { date: true };
});

I can't see the calls made to this function in the cloud function logs or in the chrome dev console Network tab. What am I doing wrong?

I tried both cloud functions emulator and live app. Still no luck!

I have been trying to debug this since the past 3 days and have lost a bit of hair and weight :/