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Accounts receivable, net - Additional information (Details) - USD ($)
Jan. 25, 2022
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Product Information [Line Items]          
Accounts receivable   $ 24,473,318 $ 10,493,069    
Allowance for doubtful accounts   $ 8,094 $ 119,199 $ 0 $ 0
Subsequent Event Member | Accounts receivable          
Product Information [Line Items]          
Accounts receivable $ 19,700,000        
Subsequent Event Member | Customer concentration risk | Accounts receivable | Customer          
Product Information [Line Items]          
Percentage of accounts receivable 80.50%