Is there a way to create multiple invoices with a single POST request to the NetSuite REST API? I'm hoping there's a way to avoid sending thousands of individual requests.
My suggestion here would be to look into N/https module in Suitescripts.
The idea here is simple. You will try to pass data using a UserEvent Script, the same data which now you are passing using Postman (or some testing application).
//Add additional code
...
var response = https.post({
url: 'https://www.testwebsite.com',
body: myPostDataObj
});
...
//Add additional code
You can use a FOR LOOP later for iterating and creating as much records as you desire.
Hope this helped. Let me know in case of issues below.