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Common Stock (Details Narrative) - USD ($) $ / shares in Units, $ in Millions |  |  |  |  |  |  | 1 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, 2022 | Apr. 30, 2021
Common stock, shares authorized |  |  |  |  |  |  |  | 100,000,000 | 100,000,000
Common stock, par value |  |  |  |  |  |  |  | $ 0.001 | $ 0.001
Common stock, shares issued |  |  |  |  |  |  |  | 55,905,213 | 52,479,051
Number of common stock shares sold |  |  |  |  | 1,542,000 |  |  |  |
Alliance Global Partners [Member] |  |  |  |  |  |  |  |  |
Number of common stock shares sold |  |  |  |  |  | 12,342,506 |  |  |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  | $ 18.7 |  |  |
Combined purchase price per share |  |  |  |  |  | $ 1.51 |  |  |
2019 ATM Facility [Member] | Alliance Global Partners [Member] |  |  |  |  |  |  |  |  |
Aggregate offering price |  |  |  |  |  | $ 25.0 |  |  |
Number of common stock shares sold |  |  |  |  |  | 17,595,472 |  |  |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  | $ 23.4 |  |  |
Combined purchase price per share |  |  |  |  |  | $ 1.33 |  |  |
Payment of sales commission |  |  |  |  |  | $ 0.8 |  |  |
2020 ATM Facility [Member] |  |  |  |  |  |  |  |  |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  |  |  | $ 75.0 |
Payment of sales commission |  |  |  |  |  |  |  | 25.0 |
2020 ATM Facility [Member] | Alliance Global Partners [Member] |  |  |  |  |  |  |  |  |
Aggregate offering price |  | $ 50.0 |  |  |  |  |  | $ 50.0 |
Number of common stock shares sold |  | 17,179,883 |  |  |  |  |  | 17,179,883 |
Proceeds from issuance or sale of equity, net of issuance costs |  |  |  |  |  |  |  | $ 50.0 |
Combined purchase price per share |  |  |  |  |  |  |  | $ 2.91 | $ 2.91
Payment of sales commission |  |  |  |  |  |  |  | $ 1.6 |
2020 ATM Facility [Member] | Alliance Global Partners [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Aggregate purchase of common stock |  | $ 100.0 |  |  |  |  |  |  |
Common Stock Purchase Agreement [Member] | Aspire Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |
Number of common stock shares sold |  |  | 6,424,205 |  |  |  | 3,722,251 | 5,025,000 |
Proceeds from issuance or sale of equity, net of issuance costs |  |  | $ 4.0 |  |  |  | $ 11.8 | $ 2.9 |
Combined purchase price per share |  |  | $ 0.63 |  |  |  | $ 3.17 | $ 0.57 |
Aggregate purchase of common stock |  |  | $ 12.5 |  |  |  |  |  |
[custom:PercentageOfOutstandingCommonStockLimitForShareholderApproval] | 19.99% |  | 19.99% |  |  |  |  |  |
[custom:StockIssuedDuringPeriodSharesCanBeIssuedBasedUponOutstandingPercentage] |  |  | 3,722,251 |  |  |  |  |  |
[custom:NumberOfAdditionalSharesThatCanBeIssuedUponShareholderApproval] | 9,864,706 |  |  |  |  |  |  |  |
[custom:SaleOfStockConsiderationReceivedPerTransactionRemaining] |  |  |  |  |  |  |  | $ 1.0 |
Common Stock Purchase Agreement [Member] | Aspire Capital Fund, LLC [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Aggregate purchase of common stock |  |  |  | $ 10.0 |  |  |  |  |

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