Trade accounts receivable, net (excluding financing receivables) is reflected in the following table (in thousands):

	June 30, 2020			September 30, 2019
Trade accounts receivable	$	14,874		$	25,144
Allowance for doubtful accounts		(1,189	)		(951	)
Total	$	13,685		$	24,193

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 accounts receivable balances. Accounts receivable balances are charged off against the allowance whenever it is probable that the receivable balance will not be recoverable.

The following table summarizes changes in the Company’s allowance for doubtful accounts for the nine months ended June 30, 2020:

Trade accounts receivable at June 30, 2020 and September 30, 2019 includes $8.3 million and $8.5 million, respectively, due from an international seismic marine customer that, as of June 30, 2020, rented a significant amount of marine nodal equipment from the Company. The Company has experienced cash collection difficulties with this customer throughout fiscal year 2019 and through the third quarter of fiscal year 2020 due to the customer’s inability to generate sufficient cash flows to pay its obligations in a timely manner. As a result of the customer’s failure to adhere to an agreed-upon payment plan, in late November 2019, the Company ceased recognizing revenue from this customer and expects to continue to do so until the customer demonstrates its ability to routinely service its debts owed to the Company in the ordinary course of business. At June 30, 2020, the total debt contractually owed by the customer to the Company is $14.0 million; however, the customer’s trade accounts receivable balance of $8.3 million on the Company’s balance sheet at June 30, 2020 excludes $5.7 million of unrecognized rental revenue and late payment penalties invoiced by the Company during the nine months ended June 30, 2020. During the nine months ended June 30, 2020, the Company received cash payments of $6.2 million from this customer, of which $3.6 million was recognized as revenue during the third quarter of fiscal year 2020. The Company has received cash payments in excess of $24 million from this customer since the beginning of fiscal year 2018.

The Company has significant concerns about the customer’s ability to ultimately settle the debts owed to the Company because of (i) its distressed financial condition, (ii) the customer’s inability to generate sufficient cash flows to fund its past operations, (iii) the customer’s failure to make payments in accordance with its promises, (iv) the belief that the distressed state of the oil and gas exploration industry caused by the recent oversupply of crude oil on the world market will further compound the difficulties facing the customer and (v) the failure by the customer to present a plausible plan to overcome the difficulties it currently faces. During fiscal year 2020, the Company recorded a reversal of an operating lease receivable and rental revenue of $8.0 million to reduce the carrying value of an operating lease receivable owed by the customer to zero.

On May 26, 2020 the Company entered into an agreement with the customer to transition $13 million of unpaid invoices and late fees into a 24-month term debt security. The debt is secured by a third in line lien on the assets owned by the customer and has an 8% interest rate with bi-annual interest and principal payments. Principal payments can be made either in cash or in-kind payments in the form of additional debt security. In-kind principal payments require a 10% premium of interest. Subsequent to June 30, 2020, the customer completed their reorganization plan and issued the debt security on July 15, 2020 with a July 14, 2022 maturity date. The customer is required to list the debt instrument on the Oslo Stock Exchange or Nordic ABM within six months. However, the actual marketability of the debt security is unknown at this time.

	June 30, 2020			September 30, 2019
Promissory notes	$	281		$	780
Sales-type lease		658			2,692
Total financing receivables		939			3,472
Unearned income:
Sales-type lease		(5	)		(55	)
Total unearned income		(5	)		(55	)
Total financing receivables, net of unearned income		934			3,417
Less current portion		(934	)		(3,233	)
Non-current financing receivables	$	—		$	184

Promissory notes receivable are generally collateralized by the products sold, and bear interest at rates ranging up to 7% per year. The promissory notes receivable (including the unrecognized $10.0 million promissory note receivable disclosed below) 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 secured promissory note with a customer. The note has a three-year term and bears interest at 7% per year. Principal and interest payments of $0.3 million are due monthly until maturity. Due to the financial condition of the customer, the note receivable is not reflected on the Company’s consolidated balance sheet due to collectability concerns. See Note 2 for more information on this sale.

The Company entered into a sales-type lease in September 2017 resulting from the sale of rental equipment. The sales-type lease has a term of three years. Future minimum lease payments required under the lease at June 30, 2020 were $0.7 million, including $5,000 of unearned income. The final future minimum lease payment is due in September 2020. Interest income earned on the lease for the three months ended June 30, 2020 and 2019 was $10,000 and $0.1 million, respectively. Interest income earned on the lease for the nine months ended June 30, 2020 and 2019 was $38,000 and $0.1 million, respectively. The ownership of the equipment will transfer to the lessee at the end of the lease term.