App Sandbox Not Enabled Error When Uploading macOS App to App Store Despite Entitlements Being Set

Question

I am developing a macOS application using AppKit. After archiving the app and attempting to upload it to the App Store, I encounter the following error:

The following issues occurred while distributing your application.
Validation failed
App sandbox not enabled. The following executables must include the "com.apple.security.app-sandbox" entitlement with a Boolean value of true in the entitlements property.

However, I have already enabled App Sandbox in my project settings, and I have verified my entitlements file.

What I have tried:

• Ensured App Sandbox is enabled under Signing & Capabilities in Xcode.
• Verified that com.apple.security.app-sandbox is set to true in my .entitlements file.
• Checked that the entitlements file is properly linked in the build settings.
• Used the codesign and codesign -d --entitlements :- commands to inspect the app binary and confirm the entitlements.
• Re-archived and re-signed the app multiple times.
• Followed various solutions from Stack Overflow and Apple Developer forums, but none have worked.

Additional Information:

• macOS Version: V 15.2
• Xcode Version: V 16.2
• App Type: Mac AppKit application (not a sandboxed helper app)

What could be causing this issue despite the entitlements being properly configured? Is there a way to debug further why App Store Connect does not recognize the sandbox entitlement?