Could someone point me in the right direction please?

I have set the design time properties for a TIBOQuery to return
records from a stored procedure (FOR SELECT ... DO ... SUSPEND), but
I get ISC error "parameter mismatch for stored procedure <name>" when
setting the query active.

So I tried with example procedure MAIL_LABEL in employee.fdb (which
takes one input parameter) but get the same error. I also tried with
TIB_Query, but this would not prepare at design time, so I could not
set the Params.

What am I doing wrong please?
D7, IBO 4.2.Ie

object IB_Connection1: TIB_Connection
PasswordStorage = psNotSecure
SQLDialect = 3
Params.Strings = (
'SERVER=abs-s01'
'PATH=C:\Program Files\Firebird\Firebird_1_5
\examples\employee.fdb'
'USER NAME=sysdba'
'PROTOCOL=TCP/IP')
SavedPassword = '.JuMbLe.01.432B0639073E0E4B49'
end

object IBOQuery1: TIBOQuery
Params = <
item
DataType = ftInteger
Name = 'cust_no'
ParamType = ptInput
Value = 1001
end>
DatabaseName =
'abs-s01:C:\Program Files\Firebird\Firebird_1_5
\examples\employee.fdb'
IB_Connection = IB_Connection1
RecordCountAccurate = True
SQL.Strings = ('select * from mail_label')
FieldOptions = []
end