diff --git a/Gemfile.lock b/Gemfile.lock
index 98d163e..c040098 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -101,7 +101,7 @@ GEM
     bootstrap-sass (3.4.1)
       autoprefixer-rails (>= 5.2.1)
       sassc (>= 2.0.0)
-    brakeman (8.0.2)
+    brakeman (8.0.4)
       racc
     builder (3.3.0)
     capybara (3.40.0)
diff --git a/app/controllers/slack/application_controller.rb b/app/controllers/slack/application_controller.rb
index e587022..43a5783 100644
--- a/app/controllers/slack/application_controller.rb
+++ b/app/controllers/slack/application_controller.rb
@@ -43,7 +43,8 @@ def open_view(view, trigger_id:)
 
   def send_message(message, channel_id:)
     SlackClient::Client.instance.chat_postMessage(channel: channel_id, blocks: message)
-  rescue Slack::Web::Api::Errors::SlackError
-    head :unprocessable_entity
+  rescue Slack::Web::Api::Errors::SlackError => e
+    Rails.logger.error "Failed to send Slack message: #{e.message}"
+    Sentry.capture_exception(e)
   end
 end
diff --git a/test/controllers/slack/puzzles_controller_test.rb b/test/controllers/slack/puzzles_controller_test.rb
new file mode 100644
index 0000000..ee183e8
--- /dev/null
+++ b/test/controllers/slack/puzzles_controller_test.rb
@@ -0,0 +1,55 @@
+require "test_helper"
+
+class Slack::PuzzlesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    ENV["SLACK_SIGNING_SECRET"] = "test_signing_secret"
+  end
+
+  test "renders ok when puzzle fails validation" do
+    params = { payload: puzzle_payload(question: "") }
+
+    post slack_puzzle_path, params: params,
+      headers: slack_headers(body: params.to_query)
+
+    assert_response :ok
+  end
+
+  test "renders ok even when Slack notification fails after puzzle is saved" do
+    # Notification failure should only log — it must not affect the response to Slack.
+    original = Slack::ApplicationController.instance_method(:send_message)
+    Slack::ApplicationController.define_method(:send_message) { |*| nil }
+
+    params = { payload: puzzle_payload(question: "What is unique about Ruby's blocks?") }
+
+    post slack_puzzle_path, params: params,
+      headers: slack_headers(body: params.to_query)
+
+    assert_response :ok
+  ensure
+    Slack::ApplicationController.define_method(:send_message, original)
+  end
+
+  private
+
+  def puzzle_payload(question: "What is Ruby?")
+    {
+      user: { id: "U123" },
+      view: {
+        state: {
+          values: {
+            question: { question: { value: question } },
+            answer: { answer: { selected_option: { value: "ruby" } } },
+            explanation: { explanation: { value: "It is a programming language." } },
+            link: { link: { value: nil } }
+          }
+        }
+      }
+    }.to_json
+  end
+
+  def slack_headers(secret: ENV["SLACK_SIGNING_SECRET"], timestamp: Time.now.to_i, body: "")
+    ts = timestamp.to_s
+    sig = "v0=" + OpenSSL::HMAC.hexdigest("SHA256", secret, "v0:#{ts}:#{body}")
+    { "X-Slack-Request-Timestamp" => ts, "X-Slack-Signature" => sig }
+  end
+end