it's not possible to do this with the decimal function, because the max amount of numbers behind the dot is 8. You should probably handle this with a string field.
To calculate with the value of this string field in a microflow, you can use the parseDecimal option.
Hi Ikhwan Afiq,
Just check the Note under that Attribute,
The precision in the database is limited to 20 digits before and 8 digits after the decimal point.
So it should be less than 8 digits behind the decimal point.
Try to reduce the right side digit.
Hope It's helps you!!