An installment sale made by a nonresident is subject to the requirements of Section 40-18-86. The initial payment of the withholding is calculated based on the purchase price less the installment note. If the seller wishes to base the withholding on the gain, the withholding is calculated on the gain that would be recognized as a result of the proceeds received at the time of the closing. The provisions of the law regarding the percentage to be withheld and the due date to file the payment voucher and make the withholding payment to the Alabama Department of Revenue apply to installment sales in the same manner as applicable to any other sale subject to withholding under Section 40-18-86. For subsequent payments, the withholding is calculated by applying 3 or 4 percent of the principal amount included in each payment, or if the gain is used to calculate withholding, by applying 3 or 4 percent of the amount of each principal payment which represents gain. The payment voucher must be filed and the payment remitted to the Department on or before the last day of the calendar month following the calendar month within which the cumulative amount withheld for the year, less any payments already made for the year, exceeds $100. If the cumulative amount withheld for the year, less any payments already made, does not exceed $100 for the calendar year, the buyer will file the payment voucher and remit the payment to the Department on or before the last day of the month following the end of the calendar year within which the tax was withheld.