diff --git a/swift-secure-enclave-tool.swift b/swift-secure-enclave-tool.swift
index 55a33b7..0eeafe3 100644
--- a/swift-secure-enclave-tool.swift
+++ b/swift-secure-enclave-tool.swift
@@ -1,6 +1,7 @@
 // Reference:
 // - https://developer.apple.com/documentation/swift/commandline/arguments
 // - https://git.hatter.ink/hatter/card-cli/src/branch/master/swift-lib/src/lib.swift
+// - https://developer.apple.com/documentation/security/secaccesscontrolcreateflags
 
 import CryptoKit
 import LocalAuthentication
@@ -206,4 +207,4 @@ if (action == "version") {
     exitWith("ok:1.0.0-20250118")
 }
 
-exitWith("err:unknown action")
+exitWith("err:invalid action")