Angular form won't post to external URL

I'm making a site that has a form that needs to do a POST to an external payment provider. However, I need to go through my component's code to check if the user is authenticated first. If not, I need to go through my webapi to update a value. Once the response is received, I can continue with the POST to the external URL. My code look like this:

 onSubmit(form: any): void {  
         //for anonymous orders, we need to store the email before we send the form
         if(this.loggedIn){
            form.submit(); 
         }
         else{
             this.cartService.updateUserEmail(this.cart.id, this.email)
                             .subscribe(() => form.submit())
         }
  }

If this.loggedIn is true, the POST works correctly. It's only when I need to call the cartService that the form.submit isn't working. Sometimes, the console shows an error, "object does not contain a method submit()", other times, I get nothing in the console....it just isn't working.

Here is the opening form tag:

<form #cartForm="ngForm" (ngSubmit)="onSubmit(cartForm)" method="post" [action]="cart.paymentUrl" >

Any help would be appreciated.

EDIT Here is the markup for my submit button, as requested:

<button type="submit">CHECKOUT</button>

Solution

The ngForm being sent to your event handler does not have a .submit() method, so you'll need to get the underlying form from either ngForm or the event so you can use its .submit() method.

For this example, I used the event.

Markup

<!-- Note that I added the $event to the handler -->    
<form #cartForm="ngForm" (ngSubmit)="onSubmit(cartForm, $event)" method="post" [action]="cart.paymentUrl" >

onSubmit(form: any, e: any): void {  
     //Note that I added 'e' and calling the event target's .submit()
     if(this.loggedIn){
        e.target.submit();
     }
     else{
         this.cartService.updateUserEmail(this.cart.id, this.email)
            .subscribe(() => {
                e.target.submit();
            })
     }
}

I stripped it down a bit, but here is a Working Plunker ("Working" as in, you'll notice the failed POST -- after 1 second -- in console to www.google.com due to cross-domain issues.)