XERO API Returns HTTP 503 when sending multiple invoices in one requests

Question

One of my clients gets HTTP 503 every time they try to send multiple invoices in one request. Is anyone else having this issue?

I am using CURL to send a request to XERO, is this message from XERO?

Below is the CURL command

curl.exe -X POST "https://api.xero.com/api.xro/2.0/Invoices" -d "@C:\Temp\RES1XEROInvoicesPOSTDATA.xml" -H "Authorization: Bearer eyJhbGciOiJSUzI1NiIsImtpZCI6IjFDQUY4RTY2NzcyRDZEQzAyOEQ2NzI2RkQwMjYxNTgxNTcwRUZDMTkiLCJ0eXAiOiJKV1QiLCJ4NXQiOiJISy1Pxxxx" -H "Accept: application/xml" -H "Xero-tenant-id: xxxxxxxxxxxxx" -D "C:\Temp\RES1RespHeader.txt" > response.txt -v -o "C:\Temp\RES1RespBody.txt"

Response Header Response Body

Thanks, Komal