ACS Atomic Increment Operator $inc Not Working ??

Hi,

I am trying to use the '$inc' atomic increment operation using the ACS '$inc', but this does not seems to work.

I used 'Update' method with the following code for custom fields 'counter':

{
    'counter': {"$inc":12}
}

Anyone had facing the same problem? Appreciate any advice on this matter.

Thank you.

Note: I am using Ti.SDK 3.4.1GA with Android SDK 4.4.2 device.