Magento 2 API Create Order As guest: {"message":"\"%fieldName\" is required. Enter and try again.","parameters":{"fieldName":"email"}} - json

Question

I'm trying to place an order via Magento 2 API as a guest, following the guidance shown here:
https://devdocs.magento.com/guides/v2.4/rest/tutorials/orders/order-create-order.html
The end point I'm using is:
https://[domain]/rest/V1/guest-carts/'.$quote_id.'/payment-information
with quote_id being the ID of the quote created initially
Steps 1-6 complete successfully with relevant response being returned as expected.
But sending the following payload (literally a copy and paste from the docs) to the above endpoint:
{
"paymentMethod": {
"method": "banktransfer"
},
"billing_address": {
"email": "jdoe#example.com",
"region": "New York",
"region_id": 43,
"region_code": "NY",
"country_id": "US",
"street": [
"123 Oak Ave"
],
"postcode": "10577",
"city": "Purchase",
"telephone": "512-555-1111",
"firstname": "Jane",
"lastname": "Doe"
}
}
Results in this error message:
{"message":""%fieldName" is required. Enter and try again.","parameters":{"fieldName":"email"}}
The email address IS obviously being supplied, and am really at a loss as to what's going wrong.
For info, the API this is being sent to is a vanilla install of Magento set up with a test product for testing purposes
Does anyone have any ideas, or at least some suggestions as to how I can debug given the not very usefulness of the error message given?

Answer 1

You are Sending POST Request so you also have to send data in POST request in json format like :{ ""id"": {}}
And have to set Content-Type:application/json in http header.