If you have a Jenkins/CI build machine like we do or just use xcodebuild/xcbuild, you might notice some CodeSign issues with your builds that look something like this:
[ERROR]Code Sign error: No code signing identities found: No valid signing identities (i.e. certificate and private key pair) matching the team ID “<my team id>” were found.
You've confirmed you have all the signing set up correctly in your extension, so what gives? Well, it turns out that XCode validates dependencies for all targets including your WatchApp target. You'll notice that the project settings give you a super barebones space for defining your target information (bundle id, team identifier, etc).
What it doesn't let you do is define various scheme level things like the plist to use, and maybe a different signing identity! Here's the solution: