IFERROR not working

I've created an intake column to count the # of days based on a date in the Approval Request Submitted column. I want to use IFERROR to remove the INVALID DATA error and replace it with a "0" (zero).

my attempts were;

=IFERROR(ISBLANK([Approval Request Completed (Date)]@row), NETDAYS([Approval Request Submitted (Date)]@row, TODAY(), "0"))) - RETURNED UNPARSEABLE

=IF(ISBLANK([Approval Request Completed (Date)]@row), NETDAYS([Approval Request Submitted (Date)]@row, IFERROR, TODAY(), "0")) - SAME RETURN CODE

=IF(IFERROR(ISBLANK([Approval Request Completed (Date)]@row), NETDAYS([Approval Request Submitted (Date)]@row, TODAY(), "0"))) - RETURNED INCORRECT ARGUMENT SET

Appreciate any assistance.