excel formula assist

Hussein_Mohamed 

I created a Lambda to generate the full 12 months:

'PaySched(salesmonths,sales,downpayment,contractpayment,years)
=LET(
    n, COUNTA(salesmonths),
    payments, years * 4 - 1,
    width, years * 12 + (n + 2),
    start_date, MIN(salesmonths),
    dates, DATE(YEAR(start_date), MONTH(start_date) + SEQUENCE(, width, 0), 1),
    GetPayments, LAMBDA(a, v,
        LET(
            sales_amt, XLOOKUP(v, salesmonths, sales),
            down_amt, sales_amt * downpayment,
            contract_amt, sales_amt * contractpayment,
            remaining, sales_amt - (down_amt + contract_amt),
            quarterly_payment, remaining / payments,
            resized, EXPAND(EXPAND(quarterly_payment, , payments, quarterly_payment), 3, , 0),
            quarterly_arr, TOROW(resized, , 1),
            upfront, HSTACK(down_amt, 0, 0, contract_amt, 0, 0),
            padding, EXPAND(0, , MONTH(v) - 1, 0),
            all_payments, HSTACK(upfront, quarterly_arr),
            outcome, IF(MONTH(v) = 1, all_payments, HSTACK(padding, all_payments)),
            IFERROR(VSTACK(a, outcome), 0)
        )
    ),
    Payment_Schedule, REDUCE(dates, salesmonths, GetPayments),
    IF(
        ROWS(salesmonths) = ROWS(sales),
        HSTACK(VSTACK("", salesmonths), Payment_Schedule),
        "Please be sure the number of months selected equals the number of sales figures selected."
    )
)