See if it helps
0-30 days =
SUMX (
SUMMARIZE (
'OINV A/R Invoice',
'OINV A/R Invoice'[DocNum],
'OINV A/R Invoice'[CardName],
'OINV A/R Invoice'[DocTotal]
),
CALCULATE (
IF (
[Invoice Age Today] <= 30,
IF ( [AmountOwed] > 0, [AmountOwed], BLANK () ),
BLANK ()
)
)
)