Trade accounts receivable, net (excluding notes receivable) are reflected in the following table (in thousands):

	June 30, 2021			September 30, 2020
Trade accounts receivable	$	12,966		$	14,090
Allowance for doubtful accounts		(482	)		(496	)
Total	$	12,484		$	13,594

The allowance for doubtful accounts represents the Company’s best estimate of probable credit losses. The Company determines the allowance based upon historical experience and a current review of its trade accounts receivable balances. Trade accounts receivable balances are charged off against the allowance whenever it is probable that the receivable balance will not be recoverable.

	June 30, 2021			September 30, 2020
Promissory notes	$	5,708		$	184
Sales-type lease		2,974			—
Total financing receivables	$	8,682			184
Unearned income:
Sales-type lease	$	(31	)		—
Total unearned income	$	(31	)		—
Total financing receivables, net of unearned income		8,651			184
Less current portion		(6,497	)		(184	)
Non-current notes receivable	$	2,154		$	—

Promissory notes receivable are generally collateralized by the products sold, and bear interest at rates ranging up to 8% per year. The promissory notes receivable mature at various times through January 2023. The Company has, on occasion, extended or renewed notes receivable as they mature, but there is no obligation to do so.

During the second quarter of fiscal year 2020, the Company partially financed a $12.5 million product sale by entering into a $10.0 million promissory note with the customer. The note has a three-year term with monthly principal and interest payments of $0.3 million. Due to the financial condition of the customer, the Company had concerns over the probable collectability of the promissory note. As a result, the promissory note was not reflected on the Company’s consolidated balance sheet through its first quarter of fiscal year 2021. During the second quarter of fiscal year 2021, as a result of a new information received from the customer, management determined that it is probable that the customer will satisfy its remaining payment obligations to the Company and recognized the promissory note on its consolidated balance sheet as of March 31, 2021. See Note 2 for more information on this matter.

During the first quarter of fiscal year 2021, the Company entered into a $13.2 million short-term promissory note with a customer related to the sale of rental equipment and an outstanding receivable balance. The note, which bore interest at 5% per annum, was paid during the three months ended March 31, 2021.

During the third quarter of fiscal year 2021, the Company entered into a sales-type lease with a customer on land-based wireless seismic equipment from its rental fleet. The lease has a term of six months. Future minimum payments required under the lease at June 30, 2021 were $3.0 million, including $31,000 of unearned income. The future minimum leases payments of $2.0 million and $1.0 million are due in fiscal year 2021 and 2022, respectively. Interest income related to the lease of $12,000 was recognized for the three and nine months ended June 30, 2021. The ownership of the equipment will transfer to the customer at the end of the lease term.