cant post an invoice from nodeJS

cant post an invoice from nodeJS

following the example from documentation https://www.zoho.com/books/api/v3/#Invoices_Create_an_invoice

it says I have to use this api 
https://books.zoho.com/api/v3/invoices?organization_id=10234695
of course with my org id in the header of my POST http request it tells me to send 
"Authorization: Zoho-authtoken ba4604e8e433g9c892e360d53463oec5" with a token I have created for zoho books then the next header
 "Content-Type: application/x-www-form-urlencoded;charset=UTF-8"
and then the data has the "requiered fields"
{
{
customer_id : 1466041000000069017 ,
date : " 2018-08-06 " ,
line_items : [
{
item_id : 1466041000000065586
}
]
} 
using the axios library to send the data but I get the 
{ code: 4, message: 'Invalid value passed for JSONString' } }

sameresult if I send the data via POSTMAN and cant find any example of this anywhere or any error reference or how to solve the issue.

thanks in advance for the help