Any idea on why for some campaigns the attribute.message property is not present

Hi There,

Our usecase is to fetch all campaigns using 2023-06-15 https://developers.klaviyo.com/en/v2023-06-15/reference/api_overview

and then use the attribute.message to retrieve the message id and then fetch the messages for each campaigns using 2023-07-15 get campaign messages https://developers.klaviyo.com/en/v2023-07-15/reference/get_campaign_message 

However, I am noticing a few requests failing with a 405  with following error message and traceid.

Endpoint (notice how it does not contain an id, as none was present in one of the campaigns)

https://a.klaviyo.com/api/campaign-messages/

{"errors":[{"id":"a8cd8e00-4966-4ea7-be7f-971838b53ad4","status":405,"code":"method_not_allowed","title":"Method \"GET\" not allowed.","detail":"Method \"GET\" not allowed.","source":{"pointer":"/data/"}}]}

Any ideas on why that could be the case?