curl --request POST \
  --url https://api.scribe-mail.com/v1/signatures/{signature_id}/integration_entities \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "integration_entity_ids": [
    "<string>"
  ]
}
'

{
  "data": {
    "assign_to_all_future_emails": true,
    "manual_email_ids": [
      "<string>"
    ],
    "integration_entity_ids": [
      "<string>"
    ],
    "conditions": [
      [
        {
          "smart_field_id": "<string>",
          "values": [
            "<string>"
          ]
        }
      ]
    ]
  }
}