diff --git a/web/api/db.php b/web/api/db.php
index f8f0084..3cc741b 100644
--- a/web/api/db.php
+++ b/web/api/db.php
@@ -61,3 +61,16 @@ function error_out(string $message, int $status = 400): never
 {
     json_out(['error' => $message], $status);
 }
+
+/**
+ * Aborts with 400 if no Clickatell API key has been configured.
+ */
+function require_api_key(): void
+{
+    $stmt = db()->prepare("SELECT setting_value FROM `system` WHERE setting_name = 'clickatell_api_key'");
+    $stmt->execute();
+    $key = $stmt->fetchColumn();
+    if ($key === false || trim((string) $key) === '') {
+        error_out('No Clickatell API key is configured. Set one in Admin → Clickatell Settings before sending or scheduling messages.', 400);
+    }
+}
diff --git a/web/api/schedule.php b/web/api/schedule.php
index 724da04..f449a23 100644
--- a/web/api/schedule.php
+++ b/web/api/schedule.php
@@ -42,6 +42,8 @@ function handle_get(): never
 
 function handle_post(): never
 {
+    require_api_key();
+
     $body       = json_body();
     $templateId = (int) ($body['template_id'] ?? 0);
     $mode       = (string) ($body['mode'] ?? '');
@@ -104,6 +106,8 @@ function handle_post(): never
 
 function handle_put(): never
 {
+    require_api_key();
+
     $id = (int) ($_GET['id'] ?? 0);
     if ($id <= 0) {
         error_out('Missing or invalid id');
diff --git a/web/api/send-now.php b/web/api/send-now.php
index 56b7733..6494b4b 100644
--- a/web/api/send-now.php
+++ b/web/api/send-now.php
@@ -16,6 +16,8 @@ if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
 // }
 
 try {
+    require_api_key();
+
     $body       = json_body();
     $customBody = trim((string) ($body['message'] ?? ''));
     $templateId = isset($body['template_id']) ? (int) $body['template_id'] : null;
diff --git a/web/schedule.html b/web/schedule.html
index c4b88d3..b041bf0 100644
--- a/web/schedule.html
+++ b/web/schedule.html
@@ -117,6 +117,11 @@
         <i class="fa-solid fa-flask me-1"></i> Sandbox mode is active — texts are tagged as a test and excluded from
         cost calculations.
       </div>
+      <div id="noApiKeyBanner" class="alert alert-danger"
+        style="display:none;font-size:0.85rem;font-weight:600;text-align:center;">
+        <i class="fa-solid fa-circle-exclamation me-1"></i> No Clickatell API key configured —
+        <a href="index.html" class="alert-link">set one in Admin settings</a> before scheduling.
+      </div>
 
       <div class="page-header">
         <h1>Schedule</h1>
@@ -161,7 +166,7 @@
           <option value="" disabled selected>Loading templates…</option>
         </select>
 
-        <button class="btn btn-primary" onclick="addSchedule()">
+        <button class="btn btn-primary" id="addScheduleBtn" onclick="addSchedule()">
           <i class="fa-solid fa-plus me-1"></i> Add to Schedule
         </button>
       </div>
@@ -516,6 +521,16 @@
     }
     checkAuth();
     document.addEventListener('visibilitychange', () => { if (document.visibilityState === 'visible') checkAuth(); });
+
+    async function checkApiKey() {
+      try {
+        const r = await fetch('/api/settings.php?key=clickatell_api_key').then(res => res.json());
+        const missing = !r.set;
+        document.getElementById('noApiKeyBanner').style.display = missing ? '' : 'none';
+        document.getElementById('addScheduleBtn').disabled = missing;
+      } catch { }
+    }
+    checkApiKey();
   </script>
 </body>
 
diff --git a/web/send-now.html b/web/send-now.html
index 6ac5125..8a132e1 100644
--- a/web/send-now.html
+++ b/web/send-now.html
@@ -103,6 +103,11 @@
         <i class="fa-solid fa-flask me-1"></i> Sandbox mode is active — texts are tagged as a test and excluded from
         cost calculations.
       </div>
+      <div id="noApiKeyBanner" class="alert alert-danger"
+        style="display:none;font-size:0.85rem;font-weight:600;text-align:center;">
+        <i class="fa-solid fa-circle-exclamation me-1"></i> No Clickatell API key configured —
+        <a href="index.html" class="alert-link">set one in Admin settings</a> before sending.
+      </div>
 
       <div class="page-header d-flex align-items-center gap-3">
         <a href="index.html" class="btn btn-sm btn-secondary">
@@ -196,6 +201,7 @@
     const countSpan = document.getElementById('recipientCount');
     const recipientsSel = document.getElementById('recipients');
     const resultEl = document.getElementById('sendResult');
+    let noApiKey = false;
 
     // ── Populate recipients from API ───────────────────────────
     async function loadRecipients() {
@@ -276,7 +282,7 @@
       sectionEl.style.visibility = empty ? 'hidden' : 'visible';
       placeholderEl.style.display = empty ? '' : 'none';
       previewEl.textContent = empty ? '' : previewText(val);
-      sendBtn.disabled = empty;
+      sendBtn.disabled = empty || noApiKey;
       resultEl.style.display = 'none';
     });
 
@@ -333,7 +339,7 @@
         <i class="fa-solid fa-circle-xmark me-2"></i>${esc(err.message)}
       </div>`;
       } finally {
-        sendBtn.disabled = msgEl.value.trim() === '';
+        sendBtn.disabled = msgEl.value.trim() === '' || noApiKey;
         sendBtn.innerHTML = '<i class="fa-solid fa-paper-plane me-2"></i>Send to <span id="recipientCount">' + countSpan.textContent + '</span> attendees';
       }
     });
@@ -384,6 +390,16 @@
     }
     checkAuth();
     document.addEventListener('visibilitychange', () => { if (document.visibilityState === 'visible') checkAuth(); });
+
+    async function checkApiKey() {
+      try {
+        const r = await fetch('/api/settings.php?key=clickatell_api_key').then(res => res.json());
+        noApiKey = !r.set;
+        document.getElementById('noApiKeyBanner').style.display = noApiKey ? '' : 'none';
+        if (noApiKey) document.getElementById('sendBtn').disabled = true;
+      } catch { }
+    }
+    checkApiKey();
   </script>
 </body>