I have the similar situation on my mac-mini now (Feb, 2024, Sonoma 14.3.1). I have several records for testflight in my keychain. And old records work well. But a new record (I created it today) doesn't work. I have these messages: dmitriy@Mini-Dmitriy IPA % xcrun altool --upload-app --type ios --file app.ipa --username dmitriy@.com --password @keychain:TESTFLIGHT_PROD --verbose 2024-02-24 17:16:24.810 Starting altool... 2024-02-24 17:16:24.813 Initializing bundle from: /Applications/Xcode.app/Contents/SharedFrameworks/ContentDeliveryServices.framework/Versions/A/Frameworks/AppStoreService.framework 2024-02-24 17:16:24.819 Will look for transporter at executable bundle relative path: /Applications/Xcode.app/Contents/SharedFrameworks/ContentDeliveryServices.framework/itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Looking for Transporter at path: /Applications/Xcode.app/Contents/SharedFrameworks/ContentDeliveryServices.framework/itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Looking for Transporter at path: /Applications/Xcode.app/Contents/Developer/usr/bin/../SharedFrameworks/ContentDeliveryServices.framework/itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Looking for Transporter at path: /Applications/Xcode.app/Contents/Developer/usr/bin/../itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Looking for Transporter at path: /Applications/Transporter.app/Contents/itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Looking for Transporter at path: /usr/local/itms/bin/iTMSTransporter 2024-02-24 17:16:24.819 Using default transporter location: /usr/local/itms/bin/iTMSTransporter 2024-02-24 17:16:24.820 Verbose logging enabled. 2024-02-24 17:16:24.833 *** Error: Failed to read legacy keychain item 'TESTFLIGHT_PROD', Error Domain=ITunesConnectFoundationErrorDomain Code=-25300 "The specified item could not be found in the keychain." UserInfo={NSLocalizedDescription=The specified item could not be found in the keychain., NSLocalizedFailureReason=The specified item could not be found in the keychain.} 2024-02-24 17:16:24.833 *** Error: altool encountered an error. 2024-02-24 17:16:24.833 *** Error: The specified item could not be found in the keychain. (-25300) And, of course, I have a valid application key. It works without @keyachain well.

Apple disappointed me.