4. ACCOUNTS RECEIVABLE, NET Accounts receivable, net, consists of the following: | | | | | | | | | As of December 31, | | | 2021 | | 2022 | Accounts receivable, gross | | $ | 5,408 | | $ | 4,311 | Less: Allowance for doubtful accounts | | | (3,150) | | | (2,890) | Accounts receivable, net | | $ | 2,258 | | $ | 1,421 |
Movement of allowance for doubtful accounts is as follows: | | | | | | | | | | | | For the years ended December 31, | | | 2020 | | 2021 | | 2022 | Beginning of year | | $ | 5,437 | | $ | 3,797 | | $ | 3,150 | Addition | | | 524 | | | 234 | | | 100 | Reverse | | | (144) | | | (875) | | | (380) | Disposal of subsidiaries | | | (2,276) | | | — | | | — | Exchange rate adjustment | | | 256 | | | (6) | | | 20 | End of year | | $ | 3,797 | | $ | 3,150 | | $ | 2,890 |
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