receivable-unbilled, a $959,754 decrease in accounts payable, and a $218,508 decrease in deferred revenue, offset by a $198,893 increase in accrued expenses, a $90,894 decrease in prepaid expenses and other current assets, and a $38,503 decrease in tax credit receivable.
For the year ended December 31, 2020, net cash used in operating activities was $288,380, which consisted of a net loss of $4,652,084 offset by non-cash charges of approximately $1,323,000 which primarily includes $774,929 related to amortization of internally developed software, a $159,000 loss on derivative liability, $143,435 of amortization of discount and debt issuance costs on Convertible Notes, $108,096 in bad debt expense, $92,866 in stock based compensation, and $44,758 related to depreciation and amortization of property and equipment.
Total changes in assets and liabilities of approximately $3,041,000 were primarily driven by a $1,951,429 increase in accrued interest, an increase of $1,054,638 in accounts payable, an increase of $873,254 in deferred revenue, an increase in accrued expenses of $282,142, and a decrease in tax credit receivable of $104,624, offset by a $800,908 increase in accounts receivable, a $226,374 increase in prepaid expenses and other current assets, and an increase in accounts receivable-unbilled of $198,185.
Investing Activities
Net cash used in investing activities was $1,037,917 and $1,102,612 for the years ended December 31, 2021 and 2020, respectively. Net cash used in investing activities for the year ended December 31, 2021 consisted of $1,035,367 of capitalization of internally developed software and $2,550 for purchase of property and equipment. Net cash used in investing activities for the year ended December 31, 2020 consisted of $1,102,186 of capitalization of internally developed software, and purchases of property and equipment of $426.
Financing Activities
Net cash provided by financing activities was $38,749,397 and $2,033,008 for the years ended December 31, 2021 and 2020, respectively. Net cash provided by financing activities for the year ended December 31, 2021 consisted of $20,999,988 of proceeds received from the issuance of common stock in connection with the PIPE, $18,000,000 of proceeds received from the issuance of common stock in connection with the IPO, $3,500,000 of proceeds received from the issuance of note payable, $2,497,501 of net proceeds from the issuance of over-allotment shares of common stock, $500,000 of proceeds received from the issuance of Bridge Notes payable, $58,648 of proceeds received from the exercise of stock options, and $992 of proceeds received from the exercise of warrants, partially offset by the $3,000,000 payment of principal to the holders of the Bridge Notes, $2,339,816 for the payment of offering costs in connection with the issuance of common stock in connection with the IPO, $1,434,999 for the payment of offering costs in connection with the issuance of common stock in connection with PIPE, and $32,917 for the payment of debt issuance costs in connection with the note payable.
Net cash provided by financing activities for the year ended December 31, 2020 consisted of proceeds received from the issuance of Bridge Notes payable totaling $1,250,000 and proceeds received from the Paycheck Protection Program of $783,008.
Effects of Inflation and Supply Chain Shortages
Our operations are heavily reliant on specimen availability, and as a result, we often receive more requests than we can fulfill. While the Company is subject to these types of supply chain constraints that are specific to the specimen industry, we have not been affected by the more common supply chain issues currently affecting the economy, specifically surrounding transportation. Due to the small size of the packages that we ship, our carriers have been able to continue making timely deliveries during the year ended December 31, 2021.
We have experienced negative effects of inflation in certain areas of our business due to the high rates of inflation in the world’s current economy. This inflation is affecting employee salaries, which account for a significant portion of our operating costs. Additionally, costs of supplies have been affected by inflation, however, these costs are not significant to the Company’s results.