Okay so very late reply and you have probably solved it (and the starter theme is no longer supported) but for anyone who comes across this issue: In your theme.yml you have to add the searchbar hook to "global_settings > hooks > modules_to_hook > displayTop" and then on the net line below "- ps_mainmenu" add "- ps_searchbar". I also had to switch to classic theme and back to make it work.
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Okay so very late reply and you have probably solved it (and the starter theme is no longer supported) but for anyone who comes across this issue: In your theme.yml you have to add the searchbar hook to "global_settings > hooks > modules_to_hook > displayTop" and then on the net line below "- ps_mainmenu" add "- ps_searchbar". I also had to switch to classes theme and back to make it work.