diff --git a/includes/zoho/class-zoho-sync.php b/includes/zoho/class-zoho-sync.php
index 62d4aeb4..a400791f 100644
--- a/includes/zoho/class-zoho-sync.php
+++ b/includes/zoho/class-zoho-sync.php
@@ -81,7 +81,30 @@ class HVAC_Zoho_Sync {
             );
         }
 
-        // Check for HTTP-level errors
+        // Check for Zoho API error codes FIRST (more specific than generic HTTP errors)
+        if (isset($response['data'][0]['code']) && !in_array($response['data'][0]['code'], array('SUCCESS', 'DUPLICATE_DATA'))) {
+            $error_msg = isset($response['data'][0]['message']) ? $response['data'][0]['message'] : $response['data'][0]['code'];
+            // Include field-level details if available
+            if (isset($response['data'][0]['details'])) {
+                $details = $response['data'][0]['details'];
+                if (isset($details['api_name'])) {
+                    $error_msg .= ' (field: ' . $details['api_name'] . ')';
+                }
+                if (isset($details['expected_data_type'])) {
+                    $error_msg .= ' (expected: ' . $details['expected_data_type'] . ')';
+                }
+                if (isset($details['info'])) {
+                    $error_msg .= ' - ' . $details['info'];
+                }
+            }
+            return array(
+                'success' => false,
+                'id' => null,
+                'error' => $error_msg
+            );
+        }
+
+        // Check for HTTP-level errors (generic fallback)
         if (isset($response['error'])) {
             return array(
                 'success' => false,
@@ -90,16 +113,6 @@ class HVAC_Zoho_Sync {
             );
         }
 
-        // Check for Zoho API error codes
-        if (isset($response['data'][0]['code']) && !in_array($response['data'][0]['code'], array('SUCCESS', 'DUPLICATE_DATA'))) {
-            $error_msg = isset($response['data'][0]['message']) ? $response['data'][0]['message'] : $response['data'][0]['code'];
-            return array(
-                'success' => false,
-                'id' => null,
-                'error' => $error_msg
-            );
-        }
-
         // Check for successful response with ID
         if (isset($response['data'][0]['details']['id'])) {
             return array(
@@ -454,9 +467,10 @@ class HVAC_Zoho_Sync {
                 $sync_succeeded = false;
 
                 // Check if contact already exists in Zoho
-                $search_response = $this->auth->make_api_request('/Contacts/search', 'GET', array(
-                    'criteria' => "(Email:equals:{$contact_data['Email']})"
-                ));
+                $search_response = $this->auth->make_api_request(
+                    '/Contacts/search?criteria=(Email:equals:' . urlencode($contact_data['Email']) . ')',
+                    'GET'
+                );
 
                 if (!empty($search_response['data'])) {
                     // Update existing contact
@@ -1334,11 +1348,25 @@ class HVAC_Zoho_Sync {
             $role = 'Trainee';
         }
 
-        return array(
+        // Last_Name is required by Zoho - fallback to display_name or username
+        $last_name = html_entity_decode(get_user_meta($user->ID, 'last_name', true), ENT_QUOTES | ENT_HTML5, 'UTF-8');
+        if (empty(trim($last_name))) {
+            $last_name = $user->display_name ?: $user->user_login;
+        }
+
+        // Sanitize phone: strip to digits and leading +, require 10+ digits for validity
+        $raw_phone = get_user_meta($user->ID, 'phone_number', true);
+        $phone_digits = preg_replace('/\D/', '', $raw_phone);
+        $phone = '';
+        if (strlen($phone_digits) >= 10) {
+            // Preserve leading + if present, otherwise just use digits
+            $phone = (strpos(trim($raw_phone), '+') === 0 ? '+' : '') . $phone_digits;
+        }
+
+        $data = array(
             'First_Name' => html_entity_decode(get_user_meta($user->ID, 'first_name', true), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
-            'Last_Name' => html_entity_decode(get_user_meta($user->ID, 'last_name', true), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
+            'Last_Name' => $last_name,
             'Email' => $user->user_email,
-            'Phone' => get_user_meta($user->ID, 'phone_number', true),
             'Title' => html_entity_decode(get_user_meta($user->ID, 'hvac_professional_title', true), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
             'Company' => html_entity_decode(get_user_meta($user->ID, 'hvac_company_name', true), ENT_QUOTES | ENT_HTML5, 'UTF-8'),
             'Lead_Source' => 'HVAC Community Events',
@@ -1348,6 +1376,13 @@ class HVAC_Zoho_Sync {
             'Years_Experience' => get_user_meta($user->ID, 'hvac_years_experience', true),
             'Certification' => get_user_meta($user->ID, 'hvac_certifications', true)
         );
+
+        // Only include Phone if we have a valid value (10+ digits)
+        if (!empty($phone)) {
+            $data['Phone'] = $phone;
+        }
+
+        return $data;
     }
     
     /**