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eBay does not like to issue multiple keysets. Please see this article:
https://developer.ebay.com/support/kb-article?KBid=1359
I have a dozen different applications and they all use the same keyset. Additionally, they are all conveniently covered by a single "compatible application" check.
If you are creating an application for someone else that will reside on their server, and you do not wish to expose your credentials to them, I would suggest they apply for their own keyset.
