Unable to authenticate on Matrix Routing v8 HereMaps API

Question

We are new to here maps and are trying (POC) for distance matrix API. We have setup our account and linked all services. Still we are getting

{
    "error": "Forbidden",
    "error_description": "These credentials do not authorize access"
}

We have tried both apiKey and Bearer token authentication. Please guide us on how to proceed further. Our sample request:

curl --location 'https://matrix.router.hereapi.com/v8/matrix?async=false&apiKey={our_api_key}' \
--header 'Content-Type: application/json' \
--data '{
    "origins": [
        {"lat": 52.52103, "lng": 13.41268},
        {"lat": 52.51628, "lng": 13.37771},
        {"lat": 52.47342, "lng": 13.40357}
    ],
    "regionDefinition": {
        "type": "autoCircle"
    },
    "matrixAttributes": ["distances"]
}
'