To fix ‘Permission Denied! You do not have permission to access this page, please refer to your system administrator.‘ error in OpenCart you should login to your OpenCart admin panel. In your browser address bar type http://yourdomain.com/admin. If you have installed your Opencart under a subfolder “store” for an example the above URL will change to http://yourdomain.com/store/admin Login using your username and password.
Navigate to System > Users > Users and edit your user.
Check which User Group the user is assigned to.
Navigate to System > Users > User Groups and edit the group for your user
All the checkboxes in both lists should be checked. Please check all the checkboxes and save the changes.
Feel free to check the detailed video tutorial below: