create an invoice stripe using google app script

Hi I followed this documentation regarding on creating an invoice on stripe

it says here that The ID of the customer who will be billed. so I created a test customer manually on stripe and now I tried this code

function testDataInvoices()
{
  var url = "https://api.stripe.com/v1/invoices";
      var params = {
      method: "post",
      headers: {Authorization: "Basic " + Utilities.base64Encode("sk_testXXXXX:")},
      payload: 
      {
        customer: "cus_JLKM93Pc6j2mxB",
      }
    };
    var res = UrlFetchApp.fetch(url, params);
    Logger.log(res.getContentText())
}

but I am getting this error

Exception: Request failed for https://api.stripe.com returned code 400. Truncated server response: { "error": { "code": "invoice_no_customer_line_items",

Can someone please enlighten me about this stripe I really just new to this API and their API is just only for node.js

#TRIED

I tried following this link

and change my code to this

function testDataInvoices()
{
  var url = "https://api.stripe.com/v1/invoices";
      var params = {
      method: "post",
      headers: {Authorization: "Basic " + Utilities.base64Encode("sk_test_XXXXXX:")},
      payload: 
      {
        "email": "paul.kevin@senren.page",
        "payment_settings": 'pm_1FWS6ZClCIKljWvsVCvkdyWg',
        "invoice_settings[default_payment_method]":'pm_1FWS6ZClCIKljWvsVCvkdyWg'
      }
    };
    var res = UrlFetchApp.fetch(url, params);
    Logger.log(res.getContentText())
}

and got this error

A few things:

• I'm not familiar with Google App Scripts — are you sure it's safe to store a secret key in such a script and you don't need an actual backend server instead? That key has to be kept private since it can be used to do anything on your Stripe account.
• In the first case, you get an error because to issue an Invoice, you have to first call /v1/invoiceitems to add some items to the customer. Then when you call /v1/invoices, which will pull those in to charge for them: https://stripe.com/docs/invoicing/integration#create-invoice-code
• in the second case you get an error because those are not valid parameters for that endpoint(if you check the link you posted, those parameters are for /v1/customers, not /v1/invoices).

I'd suggest following https://stripe.com/docs/invoicing/integration .