diff --git a/Status.md b/Status.md
index 4de1072d..96fa2a64 100644
--- a/Status.md
+++ b/Status.md
@@ -8,9 +8,49 @@
 
 ## 🎯 CURRENT SESSION - ZOHO CRM INTEGRATION SETUP (Dec 16, 2025)
 
-### Zoho CRM Integration - Staging Environment
+### Zoho CRM Integration - Production Issue (BLOCKING)
 
-**Objective:** Configure and test Zoho CRM sync implementation for staging environment.
+**Objective:** Configure and test Zoho CRM sync implementation for production environment.
+
+**Status:** 🔴 BLOCKING - Credential save hangs on production (400 Bad Request)
+
+### Active Issue - Credential Save Hanging on Production
+
+**Problem:** When saving Zoho CRM credentials at `https://upskillhvac.com/wp-admin/admin.php?page=hvac-zoho-sync`, the AJAX request returns a 400 Bad Request error and the form hangs on "Saving...".
+
+**Console Error:**
+```
+POST https://upskillhvac.com/wp-admin/admin-ajax.php 400 (Bad Request)
+```
+
+**Investigation Completed:**
+1. ✅ Fixed Client ID regex to allow lowercase letters (`[A-Z0-9]` → `[A-Za-z0-9]`)
+2. ✅ Fixed credential storage mismatch - all methods now use `HVAC_Secure_Storage`
+3. ✅ Updated `HVAC_Zoho_CRM_Auth` class to use encrypted storage consistently
+4. ✅ Updated OAuth callback to use secure storage
+5. ✅ Updated test_connection to use secure storage
+6. ✅ Deployed fixes to production - **Issue persists**
+
+**Files Modified:**
+- `includes/admin/class-zoho-admin.php` - Secure storage for credentials, fixed regex
+- `includes/zoho/class-zoho-crm-auth.php` - All credential operations use HVAC_Secure_Storage
+
+**Next Steps for Investigation:**
+1. Check PHP error logs on production server for detailed error
+2. Test AJAX endpoint directly via curl to isolate frontend vs backend issue
+3. Verify nonce generation and validation on production
+4. Check if WAF/security plugin is blocking the request
+5. Test with browser network tab to see exact request/response
+
+**Possible Causes:**
+- Server-side security rules (Cloudflare, ModSecurity) blocking POST to admin-ajax.php
+- Nonce validation failing due to caching
+- Plugin conflict on production
+- HVAC_Secure_Storage encryption key difference between environments
+
+---
+
+### Zoho CRM Integration - Staging Environment (Working)
 
 **Status:** ✅ OAuth Working, Sync Methods Implemented, Dry-Run Tested
 
diff --git a/includes/admin/class-zoho-admin.php b/includes/admin/class-zoho-admin.php
index 414f6f67..8f3ee018 100644
--- a/includes/admin/class-zoho-admin.php
+++ b/includes/admin/class-zoho-admin.php
@@ -386,7 +386,7 @@ class HVAC_Zoho_Admin {
         }
         
         // Validate Client ID format (should start with "1000.")
-        if (!preg_match('/^1000\.[A-Z0-9]+$/', $client_id)) {
+        if (!preg_match('/^1000\.[A-Za-z0-9]+$/', $client_id)) {
             wp_send_json_error(array('message' => 'Invalid Client ID format. Should start with "1000."'));
             return;
         }
@@ -557,6 +557,11 @@ class HVAC_Zoho_Admin {
             wp_die('OAuth callback missing state parameter. Possible CSRF attack.');
         }
 
+        // Load secure storage for credential handling
+        if (!class_exists('HVAC_Secure_Storage')) {
+            require_once HVAC_PLUGIN_DIR . 'includes/class-hvac-secure-storage.php';
+        }
+
         require_once HVAC_PLUGIN_DIR . 'includes/zoho/class-zoho-crm-auth.php';
         $auth = new HVAC_Zoho_CRM_Auth();
 
@@ -564,9 +569,12 @@ class HVAC_Zoho_Admin {
             wp_die('OAuth state validation failed. Please try the authorization again.');
         }
 
-        // Get credentials from WordPress options
-        $client_id = get_option('hvac_zoho_client_id', '');
-        $client_secret = get_option('hvac_zoho_client_secret', '');
+        // Get credentials using secure storage (credentials are stored encrypted)
+        if (!class_exists('HVAC_Secure_Storage')) {
+            require_once HVAC_PLUGIN_DIR . 'includes/class-hvac-secure-storage.php';
+        }
+        $client_id = HVAC_Secure_Storage::get_credential('hvac_zoho_client_id', '');
+        $client_secret = HVAC_Secure_Storage::get_credential('hvac_zoho_client_secret', '');
         
         if (empty($client_id) || empty($client_secret)) {
             wp_die('OAuth callback error: Missing client credentials. Please configure your Zoho CRM credentials first.');
@@ -609,20 +617,19 @@ class HVAC_Zoho_Admin {
             exit;
         }
         
-        // Save tokens
-        update_option('hvac_zoho_access_token', $token_data['access_token']);
+        // Save tokens using secure storage
+        HVAC_Secure_Storage::store_credential('hvac_zoho_access_token', $token_data['access_token']);
         update_option('hvac_zoho_token_expires', time() + ($token_data['expires_in'] ?? 3600));
-        
+
         // Refresh token might not be returned on subsequent authorizations
         if (isset($token_data['refresh_token']) && !empty($token_data['refresh_token'])) {
-            update_option('hvac_zoho_refresh_token', $token_data['refresh_token']);
+            HVAC_Secure_Storage::store_credential('hvac_zoho_refresh_token', $token_data['refresh_token']);
         } else {
-            $existing_refresh = get_option('hvac_zoho_refresh_token');
+            $existing_refresh = HVAC_Secure_Storage::get_credential('hvac_zoho_refresh_token', '');
             if (empty($existing_refresh)) {
                 // This is critical - we need a refresh token for long-term access
                 // Store a warning but still complete the flow
                 update_option('hvac_zoho_missing_refresh_token', true);
-            } else {
             }
         }
 
@@ -653,9 +660,12 @@ class HVAC_Zoho_Admin {
                 return;
             }
 
-            // Get credentials from WordPress options
-            $client_id = get_option('hvac_zoho_client_id', '');
-            $client_secret = get_option('hvac_zoho_client_secret', '');
+            // Get credentials using secure storage (credentials are stored encrypted)
+            if (!class_exists('HVAC_Secure_Storage')) {
+                require_once HVAC_PLUGIN_DIR . 'includes/class-hvac-secure-storage.php';
+            }
+            $client_id = HVAC_Secure_Storage::get_credential('hvac_zoho_client_id', '');
+            $client_secret = HVAC_Secure_Storage::get_credential('hvac_zoho_client_secret', '');
             
             // Check configuration before attempting connection
             if (empty($client_id)) {
@@ -679,7 +689,7 @@ class HVAC_Zoho_Admin {
             }
             
             // Check if we have stored refresh token from previous OAuth
-            $stored_refresh_token = get_option('hvac_zoho_refresh_token');
+            $stored_refresh_token = HVAC_Secure_Storage::get_credential('hvac_zoho_refresh_token', '');
             
             if (empty($stored_refresh_token)) {
                 
diff --git a/includes/zoho/class-zoho-crm-auth.php b/includes/zoho/class-zoho-crm-auth.php
index 933574b5..81f5926b 100644
--- a/includes/zoho/class-zoho-crm-auth.php
+++ b/includes/zoho/class-zoho-crm-auth.php
@@ -13,7 +13,7 @@ if (!defined('ABSPATH')) {
 }
 
 class HVAC_Zoho_CRM_Auth {
-    
+
     private $client_id;
     private $client_secret;
     private $refresh_token;
@@ -21,27 +21,32 @@ class HVAC_Zoho_CRM_Auth {
     private $access_token;
     private $token_expiry;
     private $last_error = null;
-    
+
     public function __construct() {
-        // Load credentials from WordPress options (new approach)
-        $this->client_id = get_option('hvac_zoho_client_id', '');
-        $this->client_secret = get_option('hvac_zoho_client_secret', '');
-        $this->refresh_token = get_option('hvac_zoho_refresh_token', '');
+        // Load secure storage class
+        if (!class_exists('HVAC_Secure_Storage')) {
+            require_once plugin_dir_path(dirname(__FILE__)) . 'class-hvac-secure-storage.php';
+        }
+
+        // Load credentials from WordPress options using secure storage (encrypted)
+        $this->client_id = HVAC_Secure_Storage::get_credential('hvac_zoho_client_id', '');
+        $this->client_secret = HVAC_Secure_Storage::get_credential('hvac_zoho_client_secret', '');
+        $this->refresh_token = HVAC_Secure_Storage::get_credential('hvac_zoho_refresh_token', '');
         $this->redirect_uri = get_site_url() . '/oauth/callback';
-        
+
         // Fallback to config file if options are empty (backward compatibility)
         if (empty($this->client_id) || empty($this->client_secret)) {
             $config_file = plugin_dir_path(__FILE__) . 'zoho-config.php';
             if (file_exists($config_file)) {
                 require_once $config_file;
-                
+
                 $this->client_id = empty($this->client_id) && defined('ZOHO_CLIENT_ID') ? ZOHO_CLIENT_ID : $this->client_id;
                 $this->client_secret = empty($this->client_secret) && defined('ZOHO_CLIENT_SECRET') ? ZOHO_CLIENT_SECRET : $this->client_secret;
                 $this->refresh_token = empty($this->refresh_token) && defined('ZOHO_REFRESH_TOKEN') ? ZOHO_REFRESH_TOKEN : $this->refresh_token;
                 $this->redirect_uri = defined('ZOHO_REDIRECT_URI') ? ZOHO_REDIRECT_URI : $this->redirect_uri;
             }
         }
-        
+
         // Load stored access token from WordPress options
         $this->load_access_token();
     }
@@ -354,31 +359,31 @@ class HVAC_Zoho_CRM_Auth {
     }
     
     /**
-     * Save tokens to WordPress options
+     * Save tokens to WordPress options using secure storage
      */
     private function save_tokens() {
-        update_option('hvac_zoho_refresh_token', $this->refresh_token);
+        HVAC_Secure_Storage::store_credential('hvac_zoho_refresh_token', $this->refresh_token);
         $this->save_access_token();
     }
-    
+
     /**
-     * Save access token
+     * Save access token using secure storage
      */
     private function save_access_token() {
-        update_option('hvac_zoho_access_token', $this->access_token);
+        HVAC_Secure_Storage::store_credential('hvac_zoho_access_token', $this->access_token);
         update_option('hvac_zoho_token_expiry', $this->token_expiry);
     }
-    
+
     /**
-     * Load access token from WordPress options
+     * Load access token from WordPress options using secure storage
      */
     private function load_access_token() {
-        $this->access_token = get_option('hvac_zoho_access_token');
+        $this->access_token = HVAC_Secure_Storage::get_credential('hvac_zoho_access_token', '');
         $this->token_expiry = get_option('hvac_zoho_token_expiry', 0);
-        
+
         // Load refresh token if not set
         if (!$this->refresh_token) {
-            $this->refresh_token = get_option('hvac_zoho_refresh_token');
+            $this->refresh_token = HVAC_Secure_Storage::get_credential('hvac_zoho_refresh_token', '');
         }
     }