The heading should be self explanitory.
as below that i found on forum, i don't know if this has already been suggested
""However if you would like the developers to include the option to...
Hi T123
The Multiple Attachment feature is only available in 2019.4 and later (2020.1 is around the corner), if you open Bill in this version you should see the Attachments bar at the top to open and start adding extra documents, or you can link documents from your In Tray window to existing Bills.
The link I added in the status change does have extra information on this (click here to see that post), but here's a direct link to the Help Article that gives you a more step-by-step instruction for this: Working with In Tray documents
Note: Currently the Link to Existing Bill window from In Tray will list all Bills regardless of if they have attachments, a filter is coming in 2020.1 to hide Bills with existing In Tray documents.
Cheers,
Hayden
MYOB Product Team