To close this thread. I got this to work via HTTP and also via the OpenAI module.
The problem was the audio type. I had a m4a audio file object - and I tried converting it to mp3 which worked. Which was odd because in the OpenAI documentation it says that m4a audio is an accepted format. To convert I used Adobe Media Encoder.
for your reference:
https://platform.openai.com/docs/api-reference/audio/createTranscription
All the best.