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Summary of significant accounting policies - Estimated useful lives for property, plant and equipment, net (Details) - USD ($)
6 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Accounting Policies [Line Items]    
Intangible assets estimated useful lives 3 years  
Amortization expenses $ 17,965 $ 23,239
Transportation equipment.    
Accounting Policies [Line Items]    
Estimated useful lives 4 years  
Minimum | Plant, machinery and equipment    
Accounting Policies [Line Items]    
Estimated useful lives P5Y  
Minimum | Office equipment    
Accounting Policies [Line Items]    
Estimated useful lives 3  
Maximum | Plant, machinery and equipment    
Accounting Policies [Line Items]    
Estimated useful lives P10Y  
Maximum | Office equipment    
Accounting Policies [Line Items]    
Estimated useful lives 5 years