v3.21.2
Accounts receivable, net (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Accounts receivable, net    
Accounts receivable $ 8 $ 208
Allowance for doubtful accounts (2,174) (196)
Accounts receivable, net 8 12
Balance at the beginning of the year 196 196
Addition 0 0
Written-off $ (196)  
Balance at the end of the year   $ 196