9. Long-Term Debt

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In June 2020, the Company acquired debt as part of its acquisition of United Hydrogen Group Inc. During the three and nine months ended September 30, 2023, the Company repaid $0.3 million and $5.7 million of principal related to this outstanding debt, respectively. The outstanding carrying value of the debt was $4.1 million as of September 30, 2023. The remaining outstanding principal on the debt was $5.8 million and the unamortized debt discount was $1.7 million, bearing varying interest rates ranging from 5.6% to 8.3%. The debt is scheduled to mature in 2026. As of September 30, 2023, the principal balance is due at each of the following dates as follows (in thousands):

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