login as a customer and create a campaign, in the setup step of the campaign, you will now have the option to select the attachments:
A few notes:
- Allowed file formats to upload,
- After you upload your attachments, make sure you go back to the setup screen to check if they have been properly uploaded, reason is the upload might fail silently.
- Even if you set a very high upload limit from the attachment settings, it still depends on your server if that size can be uploaded or not.