PHP Error (Version: 3.8.1)

The plugin keeps spamming the error log with the following error:

A non-numeric value encountered in /home/xxx/public_html/xxx/wp-content/plugins/master-slider/admin/includes/msp-admin-functions.php?on line 232

Below is the problematic function:

function msp_get_pro_users_num(){
    $download_num = msp_api_stats_shortcode( array( 'item-id' => '7467925', 'item-param' => 'sales_number', 'cache_in_minutes' => 1200  ) );
    return number_format_i18n( floor( ($download_num/1000) ) * 1000 ). '+';
}