(configuration required: duplicat= false and archive activatedAs mentioned before, the Kepler - Attachment fields | simple & multiple custom field can be configured to store multiple files.
Step 1: Click on Attach files Icon 
and select files.
Step 2: Choose one, or multiple files from the opening window or, drag and drop your Files.
Step 3: At this step, you can:
1. Delete files from the custom field.
2. Preview images or download other file types.
3. Add a new version (modified) of an uploaded file, the new version will be attached and the old one will be added to the archive (configuration required: Allow Duplication = false and archive is activated)
PS: When users attempt to attach empty files to an issue an "Empty File Warning" appears, the attachment process is not blocked so users can proceed as needed.
Screenshot below shows empty files "Exemple.txt" and "E.txt" . Empty means the size is 0 KB.
Step 4: The Attach File Manager controls automatically the attachments according to the administrator's configuration, and displays error messages in case of files that do not correspond to the field configuration.
Case 1: Files extensions are different from the configuration.
Case 2: The sum of all sizes is greater than the defined one.
Case 3 : One or more attached file(s) is empty ( file size equals 0 KB) differently from the configuration.
