post
https://api.campaign.episerver.net/rest//smartcampaigns//messages//attachments
Add attachments into a campaign message. With this operation you can add a single, or multiple attachments into a campaign message.
The attachments were successfully added into campaign message.
The "attachmentIds" parameter is either empty or invalid, or the campaign mailing is of type FAX.
The campaign mailing was not found.
The campaign message is not of type EMAIL.
