STOCKHOLDERS’ EQUITY (DEFICIT) (Tables)
 6 Months Ended
Jun. 30, 2020
Equity [Abstract]  
Fair Value Measurement Inputs and Valuation Techniques
The table below summarizes the valuation inputs into the MCS model for the derivative liability associated with the Unsecured Convertible Note and the Additional Convertible Note on their respective dates of issuance as of March 8, 2019 and January 10, 2020, respectively, and at the end of the period as of June 30, 2020.

 
 
Derivative Liability
 
 
June 30,
January 10,
March 8,
 
 
2020
2020
2019
Expected dividend yield
 
 
 
 
Discount rate
 
24.5
%
21.6
%
29.3
%
Expected stock price volatility
 
76.7
%
103.9
%
101.1
%
Risk-free interest rate
 
0.2
%
1.6
%
2.5
%
Expected term
 
1.1 years

2 years

2 years

Price of the underlying common stock
 
$
0.57

$
0.65

$
1.99

The table below summarizes the valuation inputs into the MCS model for the Short-Term Warrants and Long-Term Warrants at their respective dates of issuance.


Short-Term Warrants
Long-Term Warrants

March 18, 2019
March 18, 2019
May 17, 2019
Conversion price
$
4.00

$
2.56

$
2.13

Expected stock price volatility
122.0
%
85.2
%
83.4
%
Risk-free interest rate
2.5
%
2.2
%
2.2
%
Expected term
1 year

5 years

5 years

Price of the underlying common stock
$
2.48

$
2.48

$
1.58



The table below summarizes the range of valuation inputs into the Black-Scholes model for the Exchange Warrants on their date of issuance and immediately prior to the exchange.

 
Exchange Warrants
 
May 1, 2019
January 6, 2020
Conversion price
$ 2.13 - $ 2.53

$
2.13

Expected stock price volatility
84.1
%
87.3
%
Risk-free interest rate
2.2
%
1.7
%
Expected term
5 - 5.5 years

4.9 years

Price of the underlying common stock
$
1.54

$
0.58



The table below summarizes the range of valuation inputs into the Black-Scholes model for the warrant liabilities as of February 11, 2020, immediately prior to the reduction in exercise price pursuant to the Offer to Amend and Exercise.
 
Short-Term Warrants
Long-Term Warrants
 
February 11, 2020
Conversion price
$
4.00

$2.13 - $2.56

Expected stock price volatility
97.1
%
87.9% - 89.2%

Risk-free interest rate
1.6
%
1.7
%
Expected term
7 months

4 years 2 months

Price of the underlying common stock
$
0.79

$
0.79

The table below summarizes the inputs for the Black Scholes option pricing model on the date of issuance.

 
May 4, 2020
(Unaudited)
Conversion price
$
0.5894

Expected stock price volatility
73.7
%
Risk-free interest rate
0.4
%
Expected term
5
 years
Price of the underlying common stock
$
0.50
Schedule of Stock by Class
The Company had reserved shares of common stock for future issuance as follows:

 
 
June 30,
December 31,
 
 
2020
(Unaudited)
2019
Outstanding stock options
 
12,694,680

8,781,615

Warrants to purchase common stock
 
41,260,816

14,040,452

Shares issuable upon conversion of convertible debt
 
1,547,689

1,217,008

For possible future issuance under the Omnibus Plan
 
14,726,818

1,102,739

    Total common shares reserved for future issuance
 
70,230,003

25,141,814