Empty API response from Google apps script API requests

I’m integrating data from the API into Google Sheets, using the GCP tools and Apps Script.

A quirk of the built-in library routine for Apps Script, UrlFetchApp.getRequest() is that the X-Forwarded-for header is added to each request.

This appears to be OK for some endpoints - for example, a V3 api call like https://apiverson.ordoro.com/order works fine. However, several of the (v2?) API calls for objects like purchase order or goods receipt return an empty JSON body when the X-Forwarded-For header is present.

Is this a know limitation? Any help or future work-around for this?