REVENUE - Receivables and contract liabilities (Details) - USD ($) |
Dec. 31, 2021 |
Dec. 31, 2020 |
|---|---|---|
| REVENUE | ||
| Contract receivables, which are included in accounts receivable | $ 3,000,708 | $ 2,996,679 |
| Contract liabilities, which are included in Accrued expenses and other current liabilities | $ 2,251,177 | $ 1,014,652 |