Firebase Invitation not found

Dear All,

I am looking for a way to get list of customers whom I have sent invitation through the Alert trigger. Following is the code for invitation alert:

inviteCustomer(): void {
    let prompt = this.alertCtrl.create({
      title: 'Invite a customer',
      message: "Customer will be invited to join app.",
      inputs: [
        {
          name: 'name',
          placeholder: "Your customer's name",
          type: 'text'
        },
        {
          name: 'mobile',
          placeholder: "Your customer's mobile number",
          type: 'mobile'
        },
        {
          name: 'email',
          placeholder: "Your customer's email",
          type: 'email'
        },
      ],
      buttons: [
        {
          text: 'Cancel',
          handler: data => {
            console.log('Cancel clicked');
          }
        },
        {
          text: 'Save',
          handler: data => {
            this.customerProvider.inviteCustomer(data.name, data.mobile, data.email,this.retailerProfile.retailerId, 
              this.retailerProfile.retailerName).then( () => { 
                let loading = this.loadingCtrl.create();
                loading.dismiss().then(()=> {
                this.customerProvider.getPendingInvitationList();
                });
          }
              )}   
        }
      ]
    } );
    
    prompt.present();
  }

This saves the data correctly but the problem starts when I want to retrieve and conduct search for that invitation:

getInvitation(): void {
    const loading = this.loadingCtrl.create();
    if (!this.getInvitationForm.valid){
      console.log(this.getInvitationForm.value);
    } else {
      this.authProvider.getRetailerInvite(this.getInvitationForm.value.email)
        .subscribe(inviteSnapshot => {
          if (inviteSnapshot){
            this.invitation = inviteSnapshot[0];
          } else {
            console.log("No email found...");
          }
          
          loading.dismiss().then( () => { 
            this.nextSlide(); 
          });
      });
    }
    loading.present();
  }

The authProvider TS:

getRetailerInvite(email: string): FirebaseListObservable<any> {
    return this.afDatabase.list('/invite', {
      query: {
        orderByChild: 'email',
        equalTo: email,
        limitToFirst: 1
      }
    })
  }

Everytime the request returns ‘not found’ … I wanted to understand wht I am missing? The database reference or logic?