Copying Date fields

Copying Date fields

Hello

I want to copy the value of a custom field called 'feestDatum' which contains a date to the Deals Closing Date field (or stop datum in my language). I created following function, which isn't working:
  1. void Untitled_Function3 (int potentialId,  date feestDatum )
  2. resp = zoho.crm.updateRecord("Potentials", input.potentialId, {"Stop Datum" input.feestDatum});

This returns an error: Error at line number : 1 - Mismatch data type for function zoho.crm.updateRecord at argument index 2 expected data type STRING found dataType BIGINT