Invoice Dates:

Days Until Due - This determines the number of days to add to the invoice date to determine the payment due date.

Days Valid - This determines the number of days after the invoice date that this fee remains current, once exceeded the fee will be recalculated using the fee type current on the payment date.

Months Until Due - This determines the number of months to add to the invoice date to determine the payment due date (use either Days or Months).

Months Valid - This determines the number of months after the invoice date that this fee remains current, once exceeded the fee will be recalculated using the fee type current on the payment date (use either Days or Months).

Due On Date - This is a fixed payment due date, must be equal to "Valid Until Date".

Valid Until Date - This is a fixed valid until date.