Database Error

In the plugin’s Information Database Status a problem of Size is given:
Fatal error: Uncaught Error: Call to undefined function
d4p_file_size_format() in /wp-content/plugins/gd-rating-system/core/grids/database.php:40

Here’s the function in the lines 39-41.
protected function column_size( $item ) {
return d4p_file_size_format( $item->Data_length + $item->Index_length );
}

I use PHP 7.4
Wordpress 5.6
Tried different themes. The problem remains.