Webhook subscription not working with my notification URL

I’m trying to subscribe to receive Webhook notifications so I can be notified when a video finishes uploading. To do so I am using this command:

curl -X PUT --header 'Authorization: Bearer $TOKEN' \api.cloudflare/client/v4/accounts/$ACCOUNT/stream/webhook \--data '{"notificationUrl":"$WEBHOOK_NOTIFICATION_URL"}'

But the response I get is:

{
“result”: null,
“success”: false,
“errors”: [
{
“code”: 10010,
“message”: “Invalid URL”
}
],
“messages”: [
{
“code”: 10010,
“message”: “This url is not available for this service. Please try with another domain”
}
]
}

I am developing locally and using a development server on one of my computer’s ports, with the notificationUrl like 127.0.0.1:8000/my-url.
Maybe the issue is related to that? I am not sure, so please help.