diff --git a/app/Controllers/MasterController.php b/app/Controllers/MasterController.php
index e68ccee..58ce33c 100644
--- a/app/Controllers/MasterController.php
+++ b/app/Controllers/MasterController.php
@@ -794,7 +794,7 @@ class MasterController extends BaseController
                                     ->join('client', 'client_branch.client_id = client.client_id', 'left')
                                     ->where('client_docs.id', $doc_id)->get()->getRow();
             // helper('url');
-            $url ='<a href="' . generate_signed_url('preview', ['doc_id'=>md5($doc_id)], 100) . '">Preview and Approve Document</a>';
+            $url ='<a href="' . generate_signed_url('preview', ['doc_id'=>md5((string)$doc_id)], 100) . '">Preview and Approve Document</a>';
             // $businessData = $this->BranchModel->select('branches.* , business.business_name ')
             //                                     ->join('business', 'branches.business_id = business.business_id', 'left')
             //                                     ->where('branches.branch_id',$this->session->get('logged_in_staff_branch_id'))