Some Object Record Types not posting to Slack from Flow

Hi all!

I'm using the Post to Slack apex action within Flow, and whilst posting Lead records to Slack works without any issue, passing any other type of record id doesn't.

I see no errors anywhere - Debug within Flow passes through the element without issue. Nothing in Debug Logs.

Contact sharing is set to "parent" - Accounts are Public internally. So I don't think it is a sharing issue.

Any advice would be appreciated.

 Thanks,

Ross