In the Print When event of Footnote put the following:

pr_eof_check('inv_numb')

& then add the following procedure somewhere in the project:

PARAMETER zfield
holdinv=&zfield
IF NOT EOF()
SKIP 1

IF &zfield <> holdinv OR EOF()
zeof = .t.
ELSE
*-- More line items on this invoice
zeof = .f.
ENDIF

SKIP -1
ELSE
zeof = .t.
ENDIF
return zeof