API Question. How to search by lookup fields through the api

API Question. How to search by lookup fields through the api

r = zoho.crm._searchRecordsByPDC("Potentials", "CONTACTID", id.toString());
throws error {4420:"Invalid Search Column.Check it now"}
OR
r = zoho.crm._searchRecords("Potentials","(CONTACTID|=|" + id.toString() + ")");
throws error {4832:"Invalid parameter value"}

We bring some fields from the Contact to the Potential like phones and email. We need to update the Potential when the Contact is edited. So we need something like that called from the Contact whenever it's edited and those errors are coming back.

Is this a know issue? or is anything wrong in the code?