An Unexpected HTTP Error occurred during the API request

Use the following function to debug the HTTP API request, you will get to know the actual reason why the HTTP API request is failing.

Paste the following code in your theme’s function.php.

function dump_http_response( $response, $type, $transport, $args, $url ) {
    if ( is_admin() && $type == "response" )  {
        echo '<span style="color: #f00;">';
        var_dump( $response );
        echo '</span>';
    }
}
add_action( 'http_api_debug', 'dump_http_response', 1, 5 );