purchasing U.S. Treasury bills with maturities ranging from one to six months. The U.S. Treasury bills have been classified as available-for-sale securities. As of June 30, 2023, we had a balance of cash and cash equivalents of approximately $2,000,000 and available-for-sale securities of approximately $6,200,000, with a sum of both classifications totaling approximately $8,200,000. We also had working capital of approximately $8,100,000 as of June 30, 2023, and no longer have any debt that could decrease our liquidity.
Since inception, we have relied upon raising capital to finance our operations. In the six months ended June 30, 2023, we invested approximately $2.7 million of cash on developing our Marketplace technology to bring it closer to revenue feasibility. We intend to continue to use our existing cash to further develop our technology, grow our supply network, increase our marketing and sales presence, scale our operations, and for working capital and general corporate purposes.
We believe our cash and cash equivalents, along with our available-for-sale securities, together with the anticipated cash flow from operations will be sufficient to meet our working capital, and capital expenditure requirements for at least the next 12 months. The liquidity we derive from cash flows from operations is, to a large degree, predicated on our ability to process our unbilled receivables and collect our receivables in a timely manner. In the event that revenue during the next 12 months continues to fall short of our projections or if our plans or assumptions change, including if inflation begins to have a greater impact on our business or if we decide to move forward with any activities that require more outlays of cash than originally planned, we may need to raise additional capital sooner than expected.
Our ability to obtain capital to implement our growth strategy over the longer term will depend on our future operating performance, financial condition and, more broadly, on the availability of equity and debt financing. Capital availability will be affected by prevailing conditions in our industry, the global economy, the global financial markets, and other factors, many of which are beyond our control. Specifically, as a result of recent volatility and weakness in the public markets, due to, among other factors, uncertainty in the global economy and financial markets, it may be much more difficult to raise additional capital, if and when it is needed, unless the public markets become less volatile and stronger at such time that we seek to raise additional capital. In addition, any additional debt service requirements we take on could be based on higher interest rates and shorter maturities and could impose a significant burden on our results of operations and financial condition, and the issuance of additional equity securities could result in significant dilution to stockholders.
Cash Flows
Operating Activities
For the six months ended June 30, 2023, net cash used in operating activities was approximately $4,519,000 which consisted of a net loss of approximately $5,915,000 offset by non-cash charges of approximately $1,420,000, which included $935,000 related to amortization of internally developed software, $245,000 in stock-based compensation, $262,000 in bad debt expense, and $76,000 related to depreciation and amortization of property and equipment, offset by $98,000 of amortization of discount on available-for-sale securities. Total changes in assets and liabilities of approximately $23,000 were attributable to a $122,540 increase in accounts receivable, a $679,143 decrease in accounts payable, a $649,000 decrease in accrued expenses, a $77,872 decrease in operating lease liability, a $42,734 decrease in deferred revenue, offset by a $1,229,433 decrease in accounts receivables-unbilled, a $112,665 decrease in prepaid expenses and other current assets, a $77,577 decrease in right-of-use asset, and a $128,541 decrease in tax credit receivable.
For the six months ended June 30, 2022, net cash used in operating activities was approximately $3,354,000, which consisted of a net loss of approximately $4,991,000 offset by non-cash charges of approximately $1,232,000, which included $533,000 related to amortization of internally developed software, $414,000 in stock-based compensation, $270,000 in bad debt expense, $9,000 related to depreciation and amortization of property and equipment, and $6,000 of amortization of discount on the Term Loan with the Lender. Total changes in assets and liabilities of approximately $405,000 were attributable to a $475,000 decrease in accounts receivable-unbilled, a $1,073,000 decrease in accounts receivable, partially offset by a $400,000 decrease in accounts payable, a $376,000 decrease in accrued expenses, a $320,000 decrease in deferred revenue, and a $48,000 increase in prepaid expenses and other current assets.
Investing Activities
Net cash used in investing activities was approximately $8,856,000 and $777,000 for the six months ended June 30, 2023 and 2022, respectively. Net cash used in investing activities for the six months ended June 30, 2023 consisted of $2,731,507 of capitalization of internally developed software, $7,642,929 of purchase of available-for-sale securities, and $13,745 of purchases of property and