diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Audit/CertAuditEvents.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Audit/CertAuditEvents.cs
index 910bfb2b..3244a9b5 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Audit/CertAuditEvents.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Audit/CertAuditEvents.cs
@@ -28,18 +28,17 @@ public static class CertAuditEvents
     /// <see cref="AuditOutcome.Success" />); otherwise <see langword="false" /> (Outcome
     /// <see cref="AuditOutcome.Failure" />).</param>
     /// <param name="error">On failure, the error text carried in the details payload; ignored on
-    /// success (the details payload serializes <see langword="null" /> for the error field).</param>
+    /// success (the <c>error</c> field is omitted from the details payload entirely).</param>
     /// <returns>A fully populated <see cref="AuditEvent" /> with a fresh <see cref="AuditEvent.EventId" />
     /// and <see cref="AuditEvent.OccurredAtUtc" /> set to now (UTC).</returns>
     public static AuditEvent Build(
         string action, string store, string thumbprint, string actor, bool success, string? error)
     {
-        var detailsJson = JsonSerializer.Serialize(new
-        {
-            store,
-            thumbprint,
-            error = success ? null : error,
-        });
+        // On success the error field is omitted entirely (not serialized as null) so the common
+        // success-path audit row carries no dead "error" key.
+        var detailsJson = JsonSerializer.Serialize(success
+            ? (object)new { store, thumbprint }
+            : new { store, thumbprint, error });
 
         return new AuditEvent
         {
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Audit/CertAuditEventsTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Audit/CertAuditEventsTests.cs
index 68cf6f7b..ee10c8f3 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Audit/CertAuditEventsTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Audit/CertAuditEventsTests.cs
@@ -26,6 +26,7 @@ public sealed class CertAuditEventsTests
         evt.Actor.ShouldBe("alice");
         evt.Outcome.ShouldBe(AuditOutcome.Success);
         evt.EventId.ShouldNotBe(Guid.Empty);
+        evt.OccurredAtUtc.ShouldBeGreaterThan(DateTimeOffset.UtcNow.AddSeconds(-5));
         evt.DetailsJson.ShouldNotBeNull();
         evt.DetailsJson!.ShouldContain(Thumb);
     }
@@ -88,13 +89,14 @@ public sealed class CertAuditEventsTests
         evt.DetailsJson!.ShouldContain("store write failed");
     }
 
-    /// <summary>On success the error text is omitted from the details payload (it serializes null).</summary>
+    /// <summary>On success the error text AND the error key are omitted from the details payload.</summary>
     [Fact]
     public void Build_success_omits_error_text()
     {
         var evt = CertAuditEvents.Build("Trust", "rejected", Thumb, "alice", success: true, error: "ignored");
 
         evt.DetailsJson!.ShouldNotContain("ignored");
+        evt.DetailsJson!.ShouldNotContain("error");
     }
 
     /// <summary>The public Category constant matches the value stamped onto built events.</summary>