if(
greaterOrEquals(indexOf(variables('DigitAIS'), 'AIS'), 0),
if(
greaterOrEquals(
indexOf('0123456789', substring(variables('DigitAIS'), add(indexOf(variables('DigitAIS'), 'AIS'), 3), 1)),
0
),
substring(variables('DigitAIS'), indexOf(variables('DigitAIS'), 'AIS'), 7),
''
),
''
)
Yours should be:
if(
greaterOrEquals(indexOf(item()?['Subject'], 'AIS'), 0),
if(
greaterOrEquals(
indexOf('0123456789', substring(item()?['Subject'], add(indexOf(item()?['Subject'], 'AIS'), 3), 1)),
0
),
substring(item()?['Subject'], indexOf(item()?['Subject'], 'AIS'), 7),
''
),
''
)
Now based on the emptiness you can ignore the next flow action or proceed.