If you are currently passing the values as numbers in the JSON try passing them as strings instead, i.e. instead of
"Amount":39.99
try
"Amount":"39.99"
Floating point numbers can’t always represent decimals exactly (the representation in computer memory is based on powers of two rather than powers of ten), and QuickFile may be seeing the 39.99 as 39.99000000000001 or something instead, and then complaining there’s too many decimal places.