Subject never emit (next never excute) how to catch the error

Question

zip(this.selectedProviderId, this.paymentMethodId).pipe(
    switchMap(response => this.ticketsService.getProviderAndPayerCredential(response[0], response[1]))
).subscribe(
    response => {
        response.forEach(item => { 
            if (item.PortalName === "Ams Portal") { 
                this.providerCredential.PortalName = item.PortalAms;
                this.providerCredential.UserId     = item.UserId;
                this.providerCredential.Password   = item.Password;
                this.providerCredential.Link       = item.BaseUrl;
            } else { 
                this.payerCredential.PortalName = item.PayerName;
                this.payerCredential.UserId     = item.UserId;
                this.payerCredential.Password   = item.Password;
                this.payerCredential.Link       = item.BaseUrl;
            } 
        }) 
        this.portalCredentialLoading = false;
    }, 
    _error => { 
        this.portalCredentialLoading = false; 
    }
);

selectedProviderId: Subject = new Subject(); 
paymentMethodId: Subject = new Subject();

this.ticketsService.getTicketDetails(id, 'Provider').subscribe(
    data => { 
        this.selectedProviderId.next(data.Id); 
    }
);

the subscribe above never happen , then selectedProviderId never emit