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

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