1. Oracle Cloud, Administering Planning, "Importing Data": "For scheduled jobs, you must select a file from the Inbox/Outbox. For immediate jobs, you can select a file from your local computer or from the Inbox/Outbox." This directly confirms that scheduled jobs must use files from the server's inbox.
(Source: Oracle Help Center, EPM Cloud - Administering Planning, Chapter 8: Importing and Exporting Data and Metadata, Section: Importing Data.)
2. Oracle Cloud, Administering Data Management for Oracle Enterprise Performance Management Cloud, "Uploading Files to the Oracle EPM Cloud Library": "You can upload files to the server where they can be selected for import and export operations. You upload files to the inbox/outbox server folders." This establishes the inbox/outbox as the designated server location for files used in data operations.
(Source: Oracle Help Center, EPM Cloud - Administering Data Management, Chapter 2: Administering Data Management, Section: Uploading Files to the Oracle EPM Cloud Library.)