Hi
We updated some files on your site to fix the issue:
paths:
root/templates/arthur/vertex.json
root/templates/arthur/vertex/parallax_backgrounds.php
line change: 67
root/templates/arthur/vertex/admin/elements/vertex.php
line change: 100 -> 104 to verify error when saving setting style in backend
root/templates/arthur/vertex/responsive/responsive_mobile_menu/default.php
line: 53, 72
root/templates/arthur/vertex/css_and_js.php
Line 177
Kindly check.