Thank you @gulevich. I was using an Individual Key that I generated from the People tab of Users and Access. Based on your response I found Team Keys under the Integrations tab. I generated a Team Key, downloaded, and was then able run xcrun notarytool store-credentials using that key.

@mammouth2727 Unfortunately I have not...

Running above command w/ --verbose option gives: Validating your credentials... [16:48:55.556Z] Info [API] Initialized Notary API with base URL: https://appstoreconnect.apple.com/notary/v2/ [16:48:55.557Z] Info [API] Preparing GET request to URL: https://appstoreconnect.apple.com/notary/v2/test?, Parameters: [:], Custom Headers: private<Dictionary<String, String>> [16:48:55.558Z] Debug [JWT] Generating new JWT for key ID: ... zsh: trace trap xcrun notarytool store-credentials --verbose

Validating your credentials... [16:39:00.503Z] Info [API] Initialized Notary API with base URL: https://appstoreconnect.apple.com/notary/v2/ [16:39:00.505Z] Info [API] Preparing GET request to URL: https://appstoreconnect.apple.com/notary/v2/test?, Parameters: [:], Custom Headers: private<Dictionary<String, String>> [16:39:00.505Z] Debug [JWT] Generating new JWT for key ID: ... zsh: trace trap xcrun notarytool store-credentials --verbose

Run above command with --verbose option I get this: Validating your credentials... [16:39:00.503Z] Info [API] Initialized Notary API with base URL: https://appstoreconnect.apple.com/notary/v2/ [16:39:00.505Z] Info [API] Preparing GET request to URL: https://appstoreconnect.apple.com/notary/v2/test?, Parameters: [:], Custom Headers: private<Dictionary<String, String>> [16:39:00.505Z] Debug [JWT] Generating new JWT for key ID: ... zsh: trace trap xcrun notarytool store-credentials --verbose