Sort search result by custom meta data

Hi,

we would like to sort the search results by custom meta data. We added a custom checkbox. The value is properly stored in the database. We can echo the value in the listing template. Say, the meta key is “wpsl_my_checkbox”. If the checkbox is checked, the meta value “1” is stored in the database. According to https://wpstorelocator.co/document/change-search-results-order/ we can change the sort order. However, if we change line 8 to
$custom_sort[$key] = $row['wpsl_my_checkbox'];
nothing happens. If we use, for example, “id”, everything works fine. Is it possible to sort by custom meta data? How would we change the code snippet?

Thank you!