I need to call api in javascript function like below but its not taking injected services (subService) or defined variables (formData) in javascript function and getting error of undefined addSub. How should I call api in javascript function?

Please help and guide.

HTML

<button class="btn" (click)="initializePayment(item.id,item.price)">click here</button>

TS

 formData: any;
  loading: boolean = false;

  constructor(
    private subService: SubService,
    ) { }

    initializePayment(sid,amount: number) {
        this.loading = true;
        const paymentHandler = (<any>window).StripeCheckout.configure({
          key: this.stripeKey,
          locale: 'auto',
          token: function (stripeToken: any) {
            console.log({stripeToken});
            const sToken = stripeToken.id;
            this.formData = new FormData();
            this.formData.append('id', this.id);
            this.formData.append('s_id', sid);
            this.formData.append('stripeToken', sToken);
    
            this.subService.addSub(this.formData).subscribe(
              (response) => {
                this.loading = false;
                console.log('resp: ', response);
                if (response['status'] === true) {
                  this.notifyService.showSuccess(
                    'success!!',''
                  );
                  //window.location.reload();
                  this.router.navigate(['/user']);
                } else {
                  this.notifyService.showError(
                    'Something went wrong. Please try later!!!',''
                  );
                }
              },
              (error) => {
                this.notifyService.showError(
                  error,
                  'Oooops Something went wrong. Please try later!!'
                );
                this.loading = false;
              }
            );
            //alert('Stripe token generated!');
          }
        });
      
        paymentHandler.open({
          name: 'test',
          description: 'Upgrade',
          amount: amount * 100
        });
      }