apn-environment in Testfligh stuck on Production

Steps to reproduce:

1. Install & Launch App
2. When push notifications are registered, the push notification token received is a "production" push notification token rather than a "development" push notification token.

We are trying to test on the sandbox environment with development push notification tokens, however the apn-environment for all builds we release via TestFlight are being set to "production". We wish to distribute builds via TestFlight with apn-environment set to "development".

At the moment we have only found one way to run the app with apn-environment set to "development" which is to "Export" a Debug build, then manually install it on a device via iTunes on Windows machines. This method is not efficient or considered seamless enough for non-technical testers and stakeholders. They require a seamless way to receive Debug builds via TestFlight without resorting to other third-party platforms which allow us to manually upload the "Exported Debug build".

If anyone knows how to upload a "Debug" build to Testflight which will allow the user to receive a sandbox development push token with "apn-environment" set to development I would really appreciate it.