Thanks for your answer!
Yes, I am editing the appointments_report.php file.
I added a row after line 459, with this code (It does not work):
$res = mysql_query("SELECT SUM(pc_importe) AS Resultado FROM openemr_postcalendar_events WHERE pc_eventDate BETWEEN 'form_from_date' AND 'form_to_date'");
echo "Total Importe: ".$row['resultado']." ";
I have also created the “pc_importe” field in the “openemr_postcalendar_events” table
Amounts insert correctly in table, column “amount”. But it does not work, neither does any error.