995200100 - Statement - CONSOLIDATED BALANCE SHEETS link:presentationLink link:calculationLink link:definitionLink 995200200 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS link:presentationLink link:calculationLink link:definitionLink 00200 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - calc2 link:presentationLink link:calculationLink link:definitionLink 995200400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS link:presentationLink link:calculationLink link:definitionLink 00400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS - calc2 link:presentationLink link:calculationLink link:definitionLink 99940103 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES - Consolidated VIEs in the PRC (Details) link:presentationLink link:calculationLink link:definitionLink 99940401 - Disclosure - INVESTMENTS IN MARKETABLE DEBT SECURITIES (Details) link:presentationLink link:calculationLink link:definitionLink 99940501 - Disclosure - LONG-TERM INVESTMENTS (Details) link:presentationLink link:calculationLink link:definitionLink 99940601 - Disclosure - FAIR VALUE MEASUREMENTS - Assets and liabilities that are measured or disclosed at fair value on a recurring basis (Details) link:presentationLink link:calculationLink link:definitionLink 99940701 - Disclosure - PROPERTY, EQUIPMENT AND SOFTWARE, NET (Details) link:presentationLink link:calculationLink link:definitionLink 99940801 - Disclosure - ACCOUNTS PAYABLE AND OTHER CURRENT LIABILITIES (Details) link:presentationLink link:calculationLink link:definitionLink 99940904 - Disclosure - LEASE- Maturity analysis of the annual undiscounted cash flows for operating lease and finance lease liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 99941401 - Disclosure - TAXATION (Details) link:presentationLink link:calculationLink link:definitionLink 99941405 - Disclosure - TAXATION - Composition of Income Tax Expenses (Details) link:presentationLink link:calculationLink link:definitionLink 99941406 - Disclosure - TAXATION - Reconciliation (Details) link:presentationLink link:calculationLink link:definitionLink 99941408 - Disclosure - TAXATION - Deferred tax assets and liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 99941801 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - CONDENSED BALANCE SHEETS (Details) link:presentationLink link:calculationLink link:definitionLink 99941803 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Details) link:presentationLink link:calculationLink link:definitionLink 99941804 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - CONDENSED STATEMENTS OF CASH FLOWS (Details) link:presentationLink link:calculationLink link:definitionLink 995200090 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 995200105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 995200205 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 995200300 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) EQUITY link:presentationLink link:calculationLink link:definitionLink 99940101 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES - Group's subsidiaries and the consolidated VIEs (Details) link:presentationLink link:calculationLink link:definitionLink 99940102 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES - Exclusive Business Cooperation Agreements (Details) link:presentationLink link:calculationLink link:definitionLink 99940201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 99940202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, equipment and software, net (Details) link:presentationLink link:calculationLink link:definitionLink 99940203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details) link:presentationLink link:calculationLink link:definitionLink 99940204 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Segment Reporting (Details) link:presentationLink link:calculationLink link:definitionLink 99940301 - Disclosure - CONCENTRATIONS AND RISKS - Concentration of customers and suppliers (Details) link:presentationLink link:calculationLink link:definitionLink 99940303 - Disclosure - CONCENTRATIONS AND RISKS - Currency convertibility risk (Details) link:presentationLink link:calculationLink link:definitionLink 99940502 - Disclosure - LONG-TERM INVESTMENTS - Fair value (Details) link:presentationLink link:calculationLink link:definitionLink 99940702 - Disclosure - PROPERTY, EQUIPMENT AND SOFTWARE, NET - Additional information (Details) link:presentationLink link:calculationLink link:definitionLink 99941101 - Disclosure - ORDINARY SHARES - Summary of ordinary shares (Details) link:presentationLink link:calculationLink link:definitionLink 99941102 - Disclosure - ORDINARY SHARES - Voting rights of ordinary shares (Details) link:presentationLink link:calculationLink link:definitionLink 99941201 - Disclosure - CONVERTIBLE REDEEMABLE PREFERRED SHARES - Summary of movement of Preferred Shares issued (Details) link:presentationLink link:calculationLink link:definitionLink 99941202 - Disclosure - CONVERTIBLE REDEEMABLE PREFERRED SHARES - Key Terms (Details) link:presentationLink link:calculationLink link:definitionLink 99941203 - Disclosure - CONVERTIBLE REDEEMABLE PREFERRED SHARES - Warrants (Details) link:presentationLink link:calculationLink link:definitionLink 99941301 - Disclosure - SHARE-BASED COMPENSATION (Details) link:presentationLink link:calculationLink link:definitionLink 99941302 - Disclosure - SHARE-BASED COMPENSATION - Share option activities (Details) link:presentationLink link:calculationLink link:definitionLink 99941303 - Disclosure - SHARE-BASED COMPENSATION - RSUs and RSAs activities (Details) link:presentationLink link:calculationLink link:definitionLink 99941304 - Disclosure - SHARE-BASED COMPENSATION - Valuation (Details) link:presentationLink link:calculationLink link:definitionLink 99941402 - Disclosure - TAXATION - Cayman Island and U.S. Corporate Income Tax (Details) link:presentationLink link:calculationLink link:definitionLink 99941403 - Disclosure - TAXATION - Hong Kong Tax (Details) link:presentationLink link:calculationLink link:definitionLink 99941404 - Disclosure - TAXATION - PRC CIT (Details) link:presentationLink link:calculationLink link:definitionLink 99941409 - Disclosure - TAXATION - NOLs and tax credit carryforwards (Details) link:presentationLink link:calculationLink link:definitionLink 99941411 - Disclosure - TAXATION - PRC Withholding income tax on dividends (Details) link:presentationLink link:calculationLink link:definitionLink 99941501 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Amounts due from related parties (Details) link:presentationLink link:calculationLink link:definitionLink 99941502 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Amounts due to related parties (Details) link:presentationLink link:calculationLink link:definitionLink 99941503 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Revenue (Details) link:presentationLink link:calculationLink link:definitionLink 99941504 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Operating and finance lease (Details) link:presentationLink link:calculationLink link:definitionLink 99941505 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Lease cost (Details) link:presentationLink link:calculationLink link:definitionLink 99941506 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS - Interest income (Details) link:presentationLink link:calculationLink link:definitionLink 99941602 - Disclosure - NET LOSS PER SHARE - Antidilutive securities excluded from the computation of diluted net loss per share (Details) link:presentationLink link:calculationLink link:definitionLink 99941802 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - CONDENSED BALANCE SHEETS - Parenthetical (Details) link:presentationLink link:calculationLink link:definitionLink 995200305 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) EQUITY (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 995200405 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 995210101 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES link:presentationLink link:calculationLink link:definitionLink 995210201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES link:presentationLink link:calculationLink link:definitionLink 995210301 - Disclosure - CONCENTRATIONS AND RISKS link:presentationLink link:calculationLink link:definitionLink 995210401 - Disclosure - INVESTMENTS IN MARKETABLE DEBT SECURITIES link:presentationLink link:calculationLink link:definitionLink 995210501 - Disclosure - LONG-TERM INVESTMENTS link:presentationLink link:calculationLink link:definitionLink 995210601 - Disclosure - FAIR VALUE MEASUREMENTS link:presentationLink link:calculationLink link:definitionLink 995210701 - Disclosure - PROPERTY, EQUIPMENT AND SOFTWARE, NET link:presentationLink link:calculationLink link:definitionLink 995210801 - Disclosure - ACCOUNTS PAYABLE AND OTHER CURRENT LIABILITIES link:presentationLink link:calculationLink link:definitionLink 995210901 - Disclosure - LEASE link:presentationLink link:calculationLink link:definitionLink 995211001 - Disclosure - COMMITMENTS AND CONTINGENCIES link:presentationLink link:calculationLink link:definitionLink 995211101 - Disclosure - ORDINARY SHARES link:presentationLink link:calculationLink link:definitionLink 995211201 - Disclosure - CONVERTIBLE REDEEMABLE PREFERRED SHARES link:presentationLink link:calculationLink link:definitionLink 995211301 - Disclosure - SHARE-BASED COMPENSATION link:presentationLink link:calculationLink link:definitionLink 995211401 - Disclosure - TAXATION link:presentationLink link:calculationLink link:definitionLink 995211501 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS link:presentationLink link:calculationLink link:definitionLink 995211601 - Disclosure - NET LOSS PER SHARE link:presentationLink link:calculationLink link:definitionLink 995211701 - Disclosure - RESTRICTED NET ASSETS link:presentationLink link:calculationLink link:definitionLink 995211801 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION link:presentationLink link:calculationLink link:definitionLink 99920202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies) link:presentationLink link:calculationLink link:definitionLink 99930103 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 99930203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables) link:presentationLink link:calculationLink link:definitionLink 99930403 - Disclosure - INVESTMENTS IN MARKETABLE DEBT SECURITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 99930503 - Disclosure - LONG-TERM INVESTMENTS (Tables) link:presentationLink link:calculationLink link:definitionLink 99930603 - Disclosure - FAIR VALUE MEASUREMENTS (Tables) link:presentationLink link:calculationLink link:definitionLink 99930703 - Disclosure - PROPERTY, EQUIPMENT AND SOFTWARE, NET (Tables) link:presentationLink link:calculationLink link:definitionLink 99930803 - Disclosure - ACCOUNTS PAYABLE AND OTHER CURRENT LIABILITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 99930903 - Disclosure - LEASE (Tables) link:presentationLink link:calculationLink link:definitionLink 99931103 - Disclosure - ORDINARY SHARES (Tables) link:presentationLink link:calculationLink link:definitionLink 99931203 - Disclosure - CONVERTIBLE REDEEMABLE PREFERRED SHARES (Tables) link:presentationLink link:calculationLink link:definitionLink 99931303 - Disclosure - SHARE-BASED COMPENSATION (Tables) link:presentationLink link:calculationLink link:definitionLink 99931403 - Disclosure - TAXATION (Tables) link:presentationLink link:calculationLink link:definitionLink 99931503 - Disclosure - RELATED-PARTY BALANCES AND TRANSACTIONS (Tables) link:presentationLink link:calculationLink link:definitionLink 99931603 - Disclosure - NET LOSS PER SHARE (Tables) link:presentationLink link:calculationLink link:definitionLink 99931803 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION (Tables) link:presentationLink link:calculationLink link:definitionLink 99940104 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES - Consolidated VIEs in the PRC - Narrative (Details) link:presentationLink link:calculationLink link:definitionLink 99940105 - Disclosure - OPERATIONS AND PRINCIPAL ACTIVITIES - Liquidity (Details) link:presentationLink link:calculationLink link:definitionLink 99940302 - Disclosure - CONCENTRATIONS AND RISKS - Concentration of credit risk (Details) link:presentationLink link:calculationLink link:definitionLink 99940304 - Disclosure - CONCENTRATIONS AND RISKS - Foreign currency exchange rate risk (Details) link:presentationLink link:calculationLink link:definitionLink 99940602 - Disclosure - FAIR VALUE MEASUREMENTS - Activities related to fair value of warrants liability (Details) link:presentationLink link:calculationLink link:definitionLink 99940901 - Disclosure - LEASE (Details) link:presentationLink link:calculationLink link:definitionLink 99940902 - Disclosure - LEASE - Information related to operating leases and finance leases (Details) link:presentationLink link:calculationLink link:definitionLink 99940903 - Disclosure - LEASE - Information related to lease liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 99941001 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details) link:presentationLink link:calculationLink link:definitionLink 99941407 - Disclosure - TAXATION - Effects of the income tax exemption and reduction (Details) link:presentationLink link:calculationLink link:definitionLink 99941410 - Disclosure - TAXATION - Unrecognized tax benefits (Details) link:presentationLink link:calculationLink link:definitionLink 99941601 - Disclosure - NET LOSS PER SHARE - Computation of basic and diluted net loss per share (Details) link:presentationLink link:calculationLink link:definitionLink 99941701 - Disclosure - RESTRICTED NET ASSETS (Details) link:presentationLink link:calculationLink link:definitionLink 99900 - Disclosure - Standard And Custom Axis Domain Defaults link:presentationLink link:calculationLink link:definitionLink