Header not showing on website

Hi, this is my staging website under construction and I would like to insert the header that I have created with the Elementor Header & Footer Builder on all pages. It is set to show on all pages but is not showing on any page and I believe it has something to do with the message that appears under Appearance/editor: Navigation menu has been removed or is currently unavailable. How can I enable the header please? The message already appeared before installing the plugin. Thanks

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