curl --request DELETE \
  --url https://api.heyy.io/api/v2.0/contacts/{contactId}/attributes \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "externalId": "<string>"
}
'

{
  "data": {
    "id": "<string>",
    "attributes": [
      {
        "name": "<string>",
        "value": "<string>"
      }
    ]
  }
}