curl --request GET \
  --url https://api.telli.com/v2/external/contacts/{externalId} \
  --header 'Authorization: Bearer <token>'

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "type": "<unknown>",
  "externalId": "<string>",
  "externalUrl": "<string>",
  "salutation": "<string>",
  "firstName": "<string>",
  "lastName": "<string>",
  "phoneNumber": "<string>",
  "timezoneIana": "<string>",
  "email": "<string>",
  "createdAt": "2023-11-07T05:31:56Z",
  "updatedAt": "2023-11-07T05:31:56Z",
  "properties": [
    {
      "key": "<string>",
      "dataType": "string",
      "value": "<unknown>",
      "label": "<string>",
      "options": [
        {
          "value": "<string>",
          "label": "<string>",
          "description": "<string>"
        }
      ]
    }
  ]
}