Custom sort with search api I have created a ViewsSort plugin that works on a normal view (like taxonomy_term) but not on a view based on Search API : it is not present when I click on "Add sort" in BO.
This sort is used to create a custom order of content types, and I use hook_views_data_alter() to provide it to views : 

/**
 * Implements hook_views_data_alter().
 */
function mymodule_views_data_alter(array &amp;$data) {

  // works on classic view
  $data['node_field_data']['inspiration_first'] = array(
    'title' =&gt; t('Custom search sort in page tags with inspiration first'),
    'group' =&gt; t('Search'),
    'help' =&gt; t('Sort content types in this order : dossier_inspiration, dossier_conseil, produit.'),
    'sort' =&gt; array(
      'field' =&gt; 'type',
      'id' =&gt; 'inspiration_first',
    ),
  );

  // doesn't work on search api view
  $data['search_api_db_default_search_content_index_content_type']['inspiration_first'] = array(
    'title' =&gt; t('Place inspiration first for custom search'),
    'group' =&gt; t('Search'),
    'help' =&gt; t('Sort content types in this order : dossier_inspiration, dossier_conseil, produit.'),
    'sort' =&gt; array(
      'field' =&gt; 'value',
      'id' =&gt; 'inspiration_first',
    ),
  );

}


Any idea ? Some sorts like Random work also on search api and I've provided the good table, I think (search_api_db_default_search_content_index_content_type).
Go to 

Home  -> Administration  -> Configuration ->  Search and metadata  -> Search API

&amp; Edit your Index Search. Then your URL will be like below. In my case it's 

Content Search

/admin/config/search/search-api/index/content_search/

So I'm using

$data['search_api_index_content_search']['inspiration_first']

I think in ur case it will be

$data['search_api_index_search_content_index']['inspiration_first']

Please share your URL if didn't worked.