diff --git a/admin/class-coupon-admin.php b/admin/class-coupon-admin.php
index 6dfbcb0..7817529 100644
--- a/admin/class-coupon-admin.php
+++ b/admin/class-coupon-admin.php
@@ -117,13 +117,13 @@ public function options_admin()
 	public function create_coupon()
 	{
 		check_ajax_referer($this->plugin_prefix . $this->plugin_name . '_create_nonce');
-		if (!$_POST['action'] || $_POST['action'] !== 'oms_coupon_create' || !current_user_can('administrator')) {
+		if (get_request_parameter('action') !== 'oms_coupon_create' || !current_user_can('administrator')) {
 			header('Status: 403 Forbidden', true, 403);
 			wp_die();
 		}
 
 		$user_id  = get_current_user_id();
-		$code = sanitize_key($_POST['code']);
+		$code = sanitize_key(get_request_parameter('code'));
 
 		global $wpdb;
 		$findOne = $wpdb->get_row($wpdb->prepare(
@@ -137,14 +137,19 @@ public function create_coupon()
 			], 400);
 		}
 
-		$type = in_array($_POST['type'], ['percentage', 'numeric']) ? $_POST['type'] : 'percentage';
-		$value = !empty($_POST['value']) ? intval($_POST['value']) : null;
-		$limit = !empty($_POST['limit']) ? intval($_POST['limit']) : null;
-		$activated_at = !empty($_POST['activated_at']) ? tz_strtodate($_POST['activated_at']) : null;
-		$expired_at = !empty($_POST['expired_at']) ? tz_strtodate($_POST['expired_at']) : null;
+		$type = get_request_parameter('type', 'percentage');
+		$type = in_array($type, ['percentage', 'numeric'], true) ? $type : 'percentage';
+		$value = get_request_parameter('value');
+		$value = !$value ? null : intval($value);
+		$limit = get_request_parameter('limit');
+		$limit = !$limit ? null : intval($limit);
+		$activated_at = get_request_parameter('activated_at');
+		$activated_date = !$activated_at ? null : tz_strtodate($activated_at);
+		$expired_at = get_request_parameter('expired_at');
+		$expired_date = !$expired_at ? null : tz_strtodate($expired_at);
 		if (
 			!is_null($activated_at) && !is_null($expired_at)
-			&& tz_strtodate($_POST['activated_at'], true) > tz_strtodate($_POST['expired_at'], true)
+			&& tz_strtodate($activated_at, true) > tz_strtodate($expired_at, true)
 		) {
 			wp_send_json([
 				'status' => 'error',
@@ -157,8 +162,8 @@ public function create_coupon()
 			'type' => $type,
 			'value' => $value,
 			'limit' => $limit,
-			'activated_at' => $activated_at,
-			'expired_at' => $expired_at,
+			'activated_at' => $activated_date,
+			'expired_at' => $expired_date,
 			'created_by' => $user_id,
 		];
 		$wpdb->insert(
diff --git a/admin/partials/coupon-admin-table.php b/admin/partials/coupon-admin-table.php
index 046767a..97fd84d 100644
--- a/admin/partials/coupon-admin-table.php
+++ b/admin/partials/coupon-admin-table.php
@@ -187,7 +187,7 @@ protected function column_cb($item)
      */
     protected function column_code($item)
     {
-        $page = wp_unslash($_REQUEST['page']);
+        $page = get_request_parameter('page', 1);
 
         // Build hide row action.
         $hide_query_args = [
@@ -297,9 +297,13 @@ protected function get_bulk_actions()
     protected function process_bulk_action()
     {
         global $wpdb;
-        if (isset($_GET[$this->_args['singular']])) {
-            $coupon_params = wp_unslash($_GET[$this->_args['singular']]);
-            $ids = is_array($coupon_params) ? implode(',', $coupon_params) : $coupon_params;
+
+        if (isset($_REQUEST[$this->_args['singular']])) {
+            $coupon_params = get_request_parameter($this->_args['singular']);
+            $ids = is_array($coupon_params)
+                ? implode(',', array_map('intval', $coupon_params))
+                : intval($coupon_params);
+
             switch ($this->current_action()) {
                 case 'hide':
                     $wpdb->query($wpdb->prepare(
@@ -382,16 +386,18 @@ public function prepare_items()
         $this->process_bulk_action();
 
         // If no sort, default to ID.
-        $orderby     = !empty($_REQUEST['orderby']) && in_array($_REQUEST['orderby'], $sortable, true) ? $_REQUEST['orderby'] : 'ID';
-        $order       = !empty($_REQUEST['order']) && 'ASC' === strtoupper($_REQUEST['order']) ? 'ASC' : 'DESC';
+        $orderby = get_request_parameter('orderby', 'ID');
+        if (!in_array($orderby, array_keys($sortable), true)) {
+            $orderby = 'ID';
+        }
+        $order = 'ASC' === strtoupper(get_request_parameter('order')) ? 'ASC' : 'DESC';
         $orderby_sql = 'c.' . sanitize_sql_orderby("{$orderby} {$order}");
 
         /*
          * GET THE DATA!
          */
         $data = $wpdb->get_results($wpdb->prepare(
-            "
-            SELECT
+            "SELECT
                 c.ID, c.code, c.type, c.value, c.limit, c.activated_at, c.expired_at,
                 GROUP_CONCAT(u.display_name SEPARATOR ', ') AS used_by, COUNT(u.ID) AS number_of_uses
             FROM {$wpdb->prefix}oms_coupons AS c
@@ -399,10 +405,8 @@ public function prepare_items()
             LEFT JOIN {$wpdb->prefix}users AS u ON cu.user_id = u.ID
             WHERE c.active = 1
             GROUP BY c.ID, c.code, c.type, c.value, c.limit, c.activated_at, c.expired_at
-            ORDER BY %s
-            LIMIT %d OFFSET %d
-            ",
-            $orderby_sql,
+            ORDER BY {$orderby_sql}
+            LIMIT %1\$d OFFSET %2\$d",
             $per_page,
             $offset_page,
         ), ARRAY_A);
diff --git a/public/class-coupon-public.php b/public/class-coupon-public.php
index af2f8b2..f7d9c94 100644
--- a/public/class-coupon-public.php
+++ b/public/class-coupon-public.php
@@ -140,15 +140,13 @@ public function oms_shortcode_func($atts = [], $content = null, $tag = '')
 
 		global $wpdb;
 		$findOne = $wpdb->get_row($wpdb->prepare(
-			"
-			SELECT
+			"SELECT
 				c.ID, c.code, c.type, c.value, c.limit, c.activated_at, c.expired_at,
 				COUNT(cu.user_id) AS number_of_uses, GROUP_CONCAT(cu.user_id SEPARATOR ',') AS used_by_id
 			FROM {$wpdb->prefix}oms_coupons AS c
 			LEFT JOIN {$wpdb->prefix}oms_coupons_user AS cu ON cu.oms_coupon_id = c.ID
 			WHERE c.ID = %d AND c.active = 1
-			GROUP BY c.ID, c.code, c.type, c.value, c.limit, c.activated_at, c.expired_at
-			",
+			GROUP BY c.ID, c.code, c.type, c.value, c.limit, c.activated_at, c.expired_at",
 			$coupon_id,
 		), OBJECT);
 
@@ -218,13 +216,17 @@ public function options_user()
 	public function save_coupon()
 	{
 		check_ajax_referer($this->plugin_prefix . $this->plugin_name . '_save_nonce');
-		if (!$_POST['action'] || $_POST['action'] !== 'oms_coupon_save') {
+		if (get_request_parameter('action') !== 'oms_coupon_save') {
 			header('Status: 403 Forbidden', true, 403);
 			wp_die();
 		}
 
 		$user_id  = get_current_user_id();
-		$coupon_id = intval($_POST['id']);
+		$coupon_id = intval(get_request_parameter('id'));
+		if (!$coupon_id) {
+			header('Status: 400 Bad Request', true, 400);
+			wp_die();
+		}
 		$now = tz_strtodate('now');
 
 		global $wpdb;
diff --git a/public/partials/coupon-public-table.php b/public/partials/coupon-public-table.php
index 5bf6b71..9c17df6 100644
--- a/public/partials/coupon-public-table.php
+++ b/public/partials/coupon-public-table.php
@@ -188,7 +188,7 @@ protected function column_cb($item)
     protected function column_code($item)
     {
         $user_id = get_current_user_id();
-        $page = wp_unslash($_REQUEST['page']);
+        $page = get_request_parameter('page', 1);
 
         if ($item['user_id'] == $user_id) {
             // Build hide row action.
@@ -287,13 +287,16 @@ protected function process_bulk_action()
         global $wpdb;
         $user_id = get_current_user_id();
 
-        if (isset($_GET[$this->_args['singular']])) {
-            $coupon_params = wp_unslash($_GET[$this->_args['singular']]);
-            $ids = is_array($coupon_params) ? implode(',', $coupon_params) : $coupon_params;
+        if (isset($_REQUEST[$this->_args['singular']])) {
+            $coupon_params = get_request_parameter($this->_args['singular']);
+            $ids = is_array($coupon_params)
+                ? implode(',', array_map('intval', $coupon_params))
+                : intval($coupon_params);
 
             if ($this->current_action() === 'hide') {
                 $wpdb->query($wpdb->prepare(
-                    "UPDATE {$wpdb->prefix}oms_coupons_user SET active = 0 WHERE oms_coupon_id IN(%s) AND user_id = %d",
+                    "UPDATE {$wpdb->prefix}oms_coupons_user SET active = 0
+                    WHERE oms_coupon_id IN(%s) AND user_id = %d",
                     $ids,
                     $user_id,
                 ));
@@ -301,7 +304,8 @@ protected function process_bulk_action()
 
             if ($this->current_action() === 'delete' && current_user_can('administrator')) {
                 $wpdb->query($wpdb->prepare(
-                    "DELETE FROM {$wpdb->prefix}oms_coupons_user WHERE oms_coupon_id IN(%s)",
+                    "DELETE FROM {$wpdb->prefix}oms_coupons_user
+                    WHERE oms_coupon_id IN(%s)",
                     $ids,
                 ));
             }
@@ -342,7 +346,9 @@ public function prepare_items()
          */
         $total_items = $wpdb->get_var(
             "SELECT COUNT(*) FROM {$wpdb->prefix}oms_coupons_user WHERE active = 1"
-                . current_user_can('administrator') ? '' : $wpdb->prepare(" AND user_id = %d", $user_id)
+                . current_user_can('administrator')
+                ? ''
+                : $wpdb->prepare(" AND user_id = %d", $user_id)
         );
 
         /*
@@ -371,46 +377,43 @@ public function prepare_items()
         $this->process_bulk_action();
 
         // If no sort, default to user_id.
-        $orderby     = !empty($_REQUEST['orderby']) && in_array($_REQUEST['orderby'], $sortable, true) ? $_REQUEST['orderby'] : 'user_id';
-        $orderby     = ($orderby === 'saved_at' || $orderby === 'user_id'
+        $orderby = get_request_parameter('orderby', 'user_id');
+        if (!in_array($orderby, array_keys($sortable), true)) {
+            $orderby = 'user_id';
+        }
+        $alias = ($orderby === 'saved_at' || $orderby === 'user_id'
             ? 'cu.'
             : ($orderby === 'display_name' ? 'u.' : 'c.')
-        ) . $orderby;
-        $order       = !empty($_REQUEST['order']) && 'DESC' === strtoupper($_REQUEST['order']) ? 'DESC' : 'ASC';
-        $orderby_sql = sanitize_sql_orderby("{$orderby} {$order}");
+        );
+        $order = 'DESC' === strtoupper(get_request_parameter('order')) ? 'DESC' : 'ASC';
+        $orderby_sql = $alias . sanitize_sql_orderby("{$orderby} {$order}");
 
         /*
          * GET THE DATA!
          */
         if (current_user_can('administrator')) {
             $data = $wpdb->get_results($wpdb->prepare(
-                "
-                SELECT
+                "SELECT
                     c.ID, c.code, c.type, c.value, c.expired_at, cu.saved_at, cu.user_id, u.display_name
                 FROM {$wpdb->prefix}oms_coupons AS c
                 LEFT JOIN {$wpdb->prefix}oms_coupons_user AS cu ON cu.oms_coupon_id = c.ID
                 LEFT JOIN {$wpdb->prefix}users AS u ON cu.user_id = u.ID
                 WHERE cu.active = 1
-                ORDER BY %s
-                LIMIT %d OFFSET %d
-                ",
-                $orderby_sql,
+                ORDER BY {$orderby_sql}
+                LIMIT %1\$d OFFSET %2\$d",
                 $per_page,
                 $offset_page,
             ), ARRAY_A);
         } else {
             $data = $wpdb->get_results($wpdb->prepare(
-                "
-                SELECT
+                "SELECT
                     c.ID, c.code, c.type, c.value, c.expired_at, cu.saved_at, cu.user_id
                 FROM {$wpdb->prefix}oms_coupons AS c
                 LEFT JOIN {$wpdb->prefix}oms_coupons_user AS cu ON cu.oms_coupon_id = c.ID
-                WHERE cu.active = 1 AND user_id = %d
-                ORDER BY %s
-                LIMIT %d OFFSET %d
-                ",
+                WHERE cu.active = 1 AND user_id = %1\$d
+                ORDER BY {$orderby_sql}
+                LIMIT %2\$d OFFSET %3\$d",
                 $user_id,
-                $orderby_sql,
                 $per_page,
                 $offset_page,
             ), ARRAY_A);