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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Concentration of Credit Risk (Details) - Customer Concentration Risk [Member] - Three Customers [Member] - Customer
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Revenue Benchmark [Member]    
Concentration of Credit Risk [Abstract]    
Number of major customers 3 3
Concentration of credit risk 60.10% 97.40%
Accounts Receivable [Member]    
Concentration of Credit Risk [Abstract]    
Number of major customers 3 3
Concentration of credit risk 77.30% 76.10%