diff --git a/Sources/APNSTestServer/APNSTestServer.swift b/Sources/APNSTestServer/APNSTestServer.swift
index 475078d..9306dd5 100644
--- a/Sources/APNSTestServer/APNSTestServer.swift
+++ b/Sources/APNSTestServer/APNSTestServer.swift
@@ -86,6 +86,12 @@ public final class APNSTestServer: @unchecked Sendable {
         }
     }
 
+    /// A valid-hex device token that the server treats as unregistered, responding with `410 Unregistered`.
+    public static let unregisteredDeviceToken = String(repeating: "f", count: 64)
+
+    /// The `timestamp` (milliseconds since epoch) returned alongside a simulated `410 Unregistered` response.
+    public static let unregisteredTimestampMilliseconds = 1_454_096_879_000
+
     public init() {
         self.group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
     }
@@ -268,6 +274,15 @@ public final class APNSTestServer: @unchecked Sendable {
             return (.badRequest, responseHeaders, "{\"reason\":\"BadDeviceToken\"}")
         }
 
+        // Simulate an unregistered token: a valid-hex token equal to `Self.unregisteredDeviceToken`
+        // responds with `410 Unregistered` and a `timestamp`, mirroring Apple's behaviour so the
+        // `APNSError.timestamp` decoding path can be exercised.
+        if deviceToken == Self.unregisteredDeviceToken {
+            var responseHeaders = HTTPHeaders()
+            responseHeaders.add(name: "content-type", value: "application/json")
+            return (.gone, responseHeaders, "{\"reason\":\"Unregistered\",\"timestamp\":\(Self.unregisteredTimestampMilliseconds)}")
+        }
+
         // Validate required topic header
         guard headers.contains(name: "apns-topic") else {
             var responseHeaders = HTTPHeaders()
diff --git a/Tests/APNSTests/APNSClientSendTests.swift b/Tests/APNSTests/APNSClientSendTests.swift
new file mode 100644
index 0000000..3e956a6
--- /dev/null
+++ b/Tests/APNSTests/APNSClientSendTests.swift
@@ -0,0 +1,154 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the APNSwift open source project
+//
+// Copyright (c) 2024 the APNSwift project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of APNSwift project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import APNSCore
+import APNS
+import APNSTestServer
+import Crypto
+import NIOPosix
+import XCTest
+
+/// Exercises the NIO-based ``APNSClient`` send path end-to-end against ``APNSTestServer``.
+final class APNSClientSendTests: XCTestCase {
+    var server: APNSTestServer!
+    var client: APNSClient<JSONDecoder, JSONEncoder>!
+
+    override func setUp() async throws {
+        try await super.setUp()
+
+        server = APNSTestServer()
+        try await server.start(port: 0)
+
+        client = APNSClient(
+            configuration: .init(
+                authenticationMethod: .jwt(
+                    privateKey: try P256.Signing.PrivateKey(pemRepresentation: Self.jwtPrivateKey),
+                    keyIdentifier: "MY_KEY_ID",
+                    teamIdentifier: "MY_TEAM_ID"
+                ),
+                environment: .custom(url: "http://127.0.0.1", port: server.port)
+            ),
+            eventLoopGroupProvider: .shared(MultiThreadedEventLoopGroup.singleton),
+            responseDecoder: JSONDecoder(),
+            requestEncoder: JSONEncoder()
+        )
+    }
+
+    override func tearDown() async throws {
+        try await client?.shutdown()
+        try await server?.shutdown()
+        client = nil
+        server = nil
+        try await super.tearDown()
+    }
+
+    func testSendAlert_success() async throws {
+        let response = try await client.sendAlertNotification(Self.makeAlert(), deviceToken: Self.validDeviceToken)
+
+        XCTAssertNotNil(response.apnsID)
+        XCTAssertEqual(server.getSentNotifications().count, 1)
+    }
+
+    func testSendAlert_propagatesAllHeaders() async throws {
+        var alert = APNSAlertNotification(
+            alert: .init(title: .raw("title")),
+            expiration: .immediately,
+            priority: .immediately,
+            topic: "com.example.app",
+            payload: EmptyPayload()
+        )
+        alert.collapseID = "collapse-123"
+        _ = try await client.sendAlertNotification(alert, deviceToken: Self.validDeviceToken)
+
+        let sent = try XCTUnwrap(server.getSentNotifications().first)
+        XCTAssertEqual(sent.deviceToken, Self.validDeviceToken)
+        XCTAssertEqual(sent.pushType, "alert")
+        XCTAssertEqual(sent.topic, "com.example.app")
+        XCTAssertEqual(sent.priority, "10")
+        XCTAssertEqual(sent.expiration, "0")
+        XCTAssertEqual(sent.collapseID, "collapse-123")
+    }
+
+    func testSendAlert_badDeviceTokenThrowsTypedError() async throws {
+        do {
+            _ = try await client.sendAlertNotification(Self.makeAlert(), deviceToken: "not-valid")
+            XCTFail("Expected an APNSError to be thrown")
+        } catch let error as APNSError {
+            XCTAssertEqual(error.responseStatus, 400)
+            XCTAssertEqual(error.reason, .badDeviceToken)
+        }
+    }
+
+    func testSendAlert_missingTopicThrowsTypedError() async throws {
+        let request = APNSRequest(
+            message: Self.makeAlert(),
+            deviceToken: Self.validDeviceToken,
+            pushType: .alert,
+            expiration: nil,
+            priority: nil,
+            apnsID: nil,
+            topic: nil,
+            collapseID: nil
+        )
+        do {
+            _ = try await client.send(request)
+            XCTFail("Expected an APNSError to be thrown")
+        } catch let error as APNSError {
+            XCTAssertEqual(error.responseStatus, 400)
+            XCTAssertEqual(error.reason, .missingTopic)
+        }
+    }
+
+    func testSendAlert_unregisteredCarriesTimestamp() async throws {
+        do {
+            _ = try await client.sendAlertNotification(
+                Self.makeAlert(),
+                deviceToken: APNSTestServer.unregisteredDeviceToken
+            )
+            XCTFail("Expected an APNSError to be thrown")
+        } catch let error as APNSError {
+            XCTAssertEqual(error.responseStatus, 410)
+            XCTAssertEqual(error.reason, .unregistered)
+            let timestamp = try XCTUnwrap(error.timestamp)
+            XCTAssertEqual(
+                timestamp.timeIntervalSince1970,
+                Double(APNSTestServer.unregisteredTimestampMilliseconds) / 1000,
+                accuracy: 0.001
+            )
+        }
+    }
+
+    // MARK: - Helpers
+
+    private static let validDeviceToken = String(repeating: "a", count: 64)
+
+    private static func makeAlert() -> APNSAlertNotification<EmptyPayload> {
+        APNSAlertNotification(
+            alert: .init(title: .raw("title")),
+            expiration: .immediately,
+            priority: .immediately,
+            topic: "com.example.app",
+            payload: EmptyPayload()
+        )
+    }
+
+    private static let jwtPrivateKey = """
+    -----BEGIN PRIVATE KEY-----
+    MIGTAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBHkwdwIBAQQg2sD+kukkA8GZUpmm
+    jRa4fJ9Xa/JnIG4Hpi7tNO66+OGgCgYIKoZIzj0DAQehRANCAATZp0yt0btpR9kf
+    ntp4oUUzTV0+eTELXxJxFvhnqmgwGAm1iVW132XLrdRG/ntlbQ1yzUuJkHtYBNve
+    y+77Vzsd
+    -----END PRIVATE KEY-----
+    """
+}