ShipScript has been an eBay Community volunteer since 2003, specializing in HTML, CSS, Scripts, Photos, Active Content, Technical Solutions, and online Seller Tools.
eBay supports uploads to File Exchange using a CSV file through a browser or XML file from a server.
https://www.ebay.com/help/selling/ebay-tools/file-exchange?id=4096
https://pages.ebay.com/file_exchange/SMP_faq.html?id=0
eBay's API options support server uploads that use REST, JSON, SOAP, and XML.
https://developer.ebay.com/products/sell
