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Common Stock (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands |  |  |  |  |  |  | 1 Months Ended | 4 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 23, 2020 | Nov. 20, 2020 | Sep. 18, 2020 | Oct. 24, 2019 | Apr. 08, 2019 | Jan. 07, 2019 | Jan. 31, 2021 | Apr. 30, 2021 | Apr. 30, 2021 | Apr. 30, 2020
Common stock, par value |  |  |  |  |  |  |  | $ 0.001 | $ 0.001 | $ 0.001
Common stock, shares authorized |  |  |  |  |  |  |  | 100,000,000 | 100,000,000 | 100,000,000
Common stock, shares issued |  |  |  |  |  |  |  | 52,458,011 | 52,458,011 | 12,939,420
Number of common stock shares sold |  |  |  |  | 1,542,000 |  |  |  |  |
2019 ATM Facility [Member] | Alliance Global Partners [Member] |  |  |  |  |  |  |  |  |  |
Aggregate offering price |  |  |  |  |  | $ 25,000 |  |  |  |
Number of common stock shares sold |  |  |  |  |  | 17,595,472 |  |  |  |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  | $ 23,400 |  |  |  |
Combined purchase price per share |  |  |  |  |  | $ 1.33 |  |  |  |
Payment of sales commission |  |  |  |  |  | $ 800 |  |  |  |
2020 ATM Facility [Member] | Alliance Global Partners [Member] |  |  |  |  |  |  |  |  |  |
Aggregate offering price |  | $ 50,000 |  |  |  |  |  |  |  |
Number of common stock shares sold |  |  |  |  |  |  |  |  | 17,179,883 |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  |  |  |  | $ 50,000 |
Combined purchase price per share |  |  |  |  |  |  |  | $ 2.91 | $ 2.91 |
Payment of sales commission |  |  |  |  |  |  |  |  | $ 1,600 |
2020 ATM Facility [Member] | Alliance Global Partners [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Aggregate purchase of common stock |  | $ 10,000 |  |  |  |  |  |  |  |
Stock Purchase Agreement [Member] | Aspire Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |
Number of common stock shares sold |  |  | 6,424,205 |  |  |  | 3,722,251 |  |  |
Proceeds from issuance or sale of equity, net of issuance costs |  |  | $ 4,000 |  |  |  | $ 11,800 | $ 1,000 |  |
Combined purchase price per share |  |  | $ 0.63 |  |  |  | $ 3.17 |  |  |
Aggregate purchase of common stock |  |  | $ 12,500 |  |  |  |  |  |  |
Percentage of outstanding common stock limit for shareholder approval | 19.99% |  | 19.99% |  |  |  |  |  |  |
Number of shares can be issued based upon outstanding percentage |  |  | 3,722,251 |  |  |  |  |  |  |
Number of additional shares that can be issued upon shareholder approval | 9,864,706 |  |  |  |  |  |  |  |  |
Stock Purchase Agreement [Member] | Aspire Capital Fund, LLC [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Aggregate purchase of common stock |  |  |  | $ 10,000 |  |  |  |  |  |
Stock Purchase Agreement [Member] | Aspire Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |
Number of common stock shares sold |  |  |  |  |  |  |  |  | 5,025,000 |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  |  |  |  | $ 2,900 |
Combined purchase price per share |  |  |  |  |  |  |  | $ 0.57 | $ 0.57 |

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