During the years ended December 31, 2023 and 2022, the Company granted awards under the 2018 Omnibus Incentive Compensation Plan, previously named the Amended and Restated 2009 Omnibus Incentive Compensation Plan (the “2018 Plan”). The Compensation Committee of the Board of Directors administers the plans. Under the 2018 Plan, shares of common stock may be issued upon the exercise of stock options, in the form of restricted stock, or in settlement of RSUs or other awards, including awards with alternative vesting schedules such as performance-based criteria. The 2018 Plan authorizes 3,275,309 shares, of which 910,076 remain available for future grants.

During the year ended December 31, 2023 and 2022, the Board of Directors of the Company approved and the Company granted RSUs to eligible employees under the 2018 Plan, previously named the Amended and Restated 2009 Omnibus Incentive Compensation Plan (the “2018 Plan”), as annual bonus payments. During the years ended December 31, 2023 and 2022, the total charges related to bonus payments were $1.2 million and $8.8 million, respectively.

For the years ended December 31, 2023 and 2022, the following table presents total share-based compensation expense in each functional line item on the consolidated statements of operations (in thousands):


	Year Ended December 31,
	2023		2022
Cost of revenues	$	772	$	2,110
Research and development	1,526		5,369
Sales and marketing	1,215		3,528
General and administrative	3,931		6,868
Total	$	7,444	$	17,875

The Compensation Committee of the Board of Directors determines eligibility, vesting schedules and exercise prices for stock options granted. For performance stock awards subject to market-based vesting conditions, fair values are determined using the Monte-Carlo simulation model. Stock options generally have a term of ten years and vest over a three- to four-year period.

The following table presents the weighted-average assumptions used in the Black-Scholes valuation model by the Company in calculating the fair value of each stock option granted:


	Year Ended December 31,
	2023		2022
Expected dividend yield	—	%	—	%
Risk-free interest rate	4.3	%	1.8	%
Volatility	174	%	78	%
Expected term (in years)	4.4		5.7

The weighted-average fair value of stock option awards granted during the years ended December 31, 2023 and 2022 was $3.16 and $29.10, respectively.

The following table summarizes the Company’s stock option activity for the years ended December 31, 2023 and 2022 (dollars in thousands, except per share data):


	Stock Options Outstanding	Weighted-Average Exercise Price Per Option		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding — December 31, 2021	808,579	$	48.05
Granted	150,500	46.30
Exercised	(37,069)	13.70
Canceled	(108,714)	79.65
Outstanding — December 31, 2022	813,296	$	46.50
Granted	82,825	4.13
Exercised	—	—
Canceled	(350,249)	38.39
Outstanding — December 31, 2023	545,872	$	44.16	6.30	$	1
Vested and Expected to Vest — December 31, 2023	504,839	$	45.74	6.08	$	—
Exercisable — December 31, 2023	365,246	$	49.57	5.07	$	—

The total intrinsic value of stock options exercised to purchase common stock during the years ended December 31, 2022 was approximately $3.7 million.

As of December 31, 2023, total unrecognized share-based compensation expense related to non-vested stock options was $3.0 million, which is expected to be recognized over a weighted-average period of approximately 2.78 years. The Company recognized approximately $4.0 million and $5.9 million of share-based compensation expense related to the vesting of stock option awards during the years ended December 31, 2023 and 2022, respectively.

Pursuant to the 2018 Plan and the 2015 Plan, the Company may issue RSUs that, upon satisfaction of vesting conditions, allow recipients to receive common stock. Issuances of such awards reduce common stock available under the 2018 Plan and 2015 Plan for stock incentive awards. The Company measures compensation cost associated with grants of RSUs at fair value, which is generally the closing price of the Company’s stock on the date of grant. RSUs generally vest over a three- to four-year period.


	Number of Shares	Weighted-Average Grant-Date Fair Value
Non-vested — December 31, 2021	124,772	76.54
Granted	254,405	45.08
Vested	(227,882)	45.32
Forfeited	(33,458)	34.52
Non-vested — December 31, 2022	117,837	73.30
Granted	366,713	5.78
Vested	(246,706)	12.92
Forfeited	(34,836)	39.77
Non-vested — December 31, 2023	203,008	19.84

During the years ended December 31, 2023 and 2022, the total fair value of shares vested was $1.2 million and $9.5 million, respectively.

As of December 31, 2023, there was $2.3 million of unrecognized share-based compensation expense related to non-vested RSUs, which is expected to be recognized over a weighted-average period of 1.39 years. The Company recognized approximately $3.3 million and $11.7 million of share-based compensation expense related to the vesting of RSUs during the years ended December 31, 2023 and 2022, respectively.

The ESPP permits eligible employees of the Company to purchase newly issued shares of common stock, at a price equal to 85% of the lower of the fair market value on (i) the first day of the offering period or (ii) the last day of each six-month purchase period, through payroll deductions of up to 10% of their annual cash compensation. Under the ESPP, a maximum of 532,400 shares of common stock may be purchased by eligible employees.

During the years ended December 31, 2023 and 2022, the Company issued 64,150 shares and 52,567 shares, respectively, under the ESPP. The Company recognized approximately $0.1 million and $0.3 million of share-based compensation expense related to the ESPP during the years ended December 31, 2023 and 2022, respectively.