Transcription result returns Access denied due to invalid subscription key or wrong API endpoint?

Question

I'm trying to run a batch transcription based on the example here.

I have extracted my subscription key via the screenshot attached:

and am trying to run the code via:

import requests
import json

subscription_key = "<KEY VIA SCREENSHOT>" 
service_region = "westus"

endpoint = "https://westus.api.cognitive.microsoft.com/speechtotext/v3.1/transcriptions"

headers = {
    "Ocp-Apim-Subscription-Key": subscription_key,
    "Content-Type": "application/json"
}

body = {
  "contentUrls": [
        "https://crbn.us/hello.wav",
        "https://crbn.us/whatstheweatherlike.wav"
  ],
  "properties": {
    "diarizationEnabled": True,
    "wordLevelTimestampsEnabled": True,
    "displayFormWordLevelTimestampsEnabled": True,
    "channels": [
      0,
      1
    ],
    "punctuationMode": "DictatedAndAutomatic",
    "profanityFilterMode": "Masked",
    "diarization": {
      "speakers": {
        "minCount": 1,
        "maxCount": 3
      }
    }
  },
  "locale": "en-US",
  "displayName": "test"
}

response = requests.post(endpoint, headers=headers, data=json.dumps(body))

# Check the response
if response.status_code == 201: 
    print("Transcription request submitted successfully!")
    response_data = response.json()
    print("Full response data:")
    print(json.dumps(response_data, indent=2)) 
    transcription_id = response_data['self'].split('/')[-1]
    print(f"Transcription ID: {transcription_id}")
else:
    print(f"Failed to submit transcription request. Status code: {response.status_code}")
    try:
        print(response.json())
    except json.JSONDecodeError:
        print(response.text)

This seems to be able to connect to the API and returns a transcription ID, but clicking into the links generated gives:

{"error":{"code":"401","message":"Access denied due to invalid subscription key or wrong API endpoint. Make sure to provide a valid key for an active subscription and use a correct regional API endpoint for your resource."}}

I have tried regenerating the API keys and am using the same sample data as the example - what is wrong with my code?