It had to work @partners. The new Unity SDK that supports sapphire_mainnet isn’t released yet. And that was the problem in your case as you had created a fresh project on sapphire_mainnet which wouldn’t have worked until the next release.
Hence, I advised you to switch to mainnet for now i.e. legacy mainnet.
Once the new version is released, you’ll be able to use sapphire _mainnet as the network value.