To get the actual file for an attachment, you can use this endpoint.

HTTP-Method

GET

Path

/api/rest/v3/frontend/attachments/{attachmentId}/content

Authentification

User Access Token

Path Parameter

attachmentId

Query Parameter

-none-

Responses

Action	Response	Description
success	303	You’ll get a redirect to the file
authorization error	401 / 403	See here and here for details.
not found	404 – { “code”: “get_file_error”, “message”:”No attachment with id X found” }	No attachment could be found for the given ID

Example call with curl and user access token