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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentrations and Credit Risk (Details)
12 Months Ended
Sep. 30, 2020
HKD ($)
Sep. 30, 2018
Sep. 30, 2020
HKD ($)
Sep. 30, 2019
HKD ($)
Sep. 30, 2018
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Concentration Risk [Line Items]              
Cash and cash equivalents, certificates of deposit and restricted cash were on deposit at financial institutions not subject to insured           $ 10,847,959 $ 3,623,348
Cash and cash equivalents deposited in financial institutions           1,018,726 0
Cash and cash equivalents deposited in financial institutions annual limit $ 500,000   $ 500,000 $ 500,000   $ 65,000 $ 65,000
Customer | Customer One | Revenue              
Concentration Risk [Line Items]              
Concentration risk (in percent)     18.00% 15.00%      
Customer | Customer One | Accounts Receivable              
Concentration Risk [Line Items]              
Concentration risk (in percent) 35.00% 45.00%   46.00%      
Customer | Customer Two | Revenue              
Concentration Risk [Line Items]              
Concentration risk (in percent)     11.00%        
Customer | Customer Two | Accounts Receivable              
Concentration Risk [Line Items]              
Concentration risk (in percent) 16.00% 24.00%   30.00%      
Customer | Customer Three | Revenue              
Concentration Risk [Line Items]              
Concentration risk (in percent)     10.00%        
Customer | Customer Three | Accounts Receivable              
Concentration Risk [Line Items]              
Concentration risk (in percent) 14.00%            
Supplier | Supplier One | Purchases              
Concentration Risk [Line Items]              
Concentration risk (in percent)     11.00% 13.00% 19.00%    
Supplier | Supplier Two | Purchases              
Concentration Risk [Line Items]              
Concentration risk (in percent)     10.00% 10.00% 14.00%