get https://connect.penbox.io/v1/attachments/ (COPY)
Retrieve an Attachment file in base64
Use the correct Accept header
It is important to not put Accept : application/json to receive the bytes. Otherwise you will retrieve the JSON object.
Be sure to use the attachment id, not the request id
The data returned in data is in base64. You can use online tools (example) to decode the returned data.