Zoho - Worklfow, custom function

Zoho - Worklfow, custom function

Hi all,

I have a workflow triggered when a potential is win. It copies (with a custom function) the Potential_closing_date into a custom field in account named ''last_closing_date''. This works fine, here is the custom function :

acctIdStr=input.acctId.toString();
mp=map();
mp.put("Last closing date",input.closing_date);
update = zoho.crm.updateRecord(("Accounts"),acctIdStr,mp);
info mp;
info update;

I also built a custom function to recopie the ''last_closing_date'' field into all my contacts. Here is the code :

acctIdStr=input.acctId.toString();
relatedcontacts = zoho.crm.getRelatedRecords("Contacts",("Accounts"),acctIdStr);
info relatedcontacts;
for each ele in relatedcontacts
{
contId=ifnull(ele.get("CONTACTID"),"");
mp=map();
mp.put("Last closing date",input.closing_date);
update = zoho.crm.updateRecord("Contacts",contId,mp);
info mp;
info update;
}

The function works well, my problem is I cannot find the right workflow to trigger it automatically.
I tried with ''when the account is create/edit'', thinking it would work. 
It doesn't work, I think, because it's a worklfow that edit the ''last_closing_date'' and not a human, so the worklfow to copie the information form Accounts to Contacts, doesn't happen...

How can I get around that ? 
I don't want to have to manually update the account with a dumb filed just to make sure the information is updated... And I don't want to do it based on the ''last_closing_date'' date/time, because I need my contact to be updated every time without thinking about it.

Thank you all for your help!