WordPress customizer loading blank page

I'm unable to load WordPress customizer, no matter the theme I have activated on the site.

Deactivated all plugins, increased WordPress and PHP memory as well as max_execution_time but still getting the same error:
Refused to display 'http://domain.com/?customize_changeset_uuid=a9594047-8ba4-4244-bc92-4cc2b2e08b4c&customize_theme=petit-child&customize_messenger_channel=preview-0' in a frame because an ancestor violates the following Content Security Policy directive: "frame-ancestors http://domain.com.com".