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Disclosure - PROPERTY AND EQUIPMENT, NET (Details) link:presentationLink link:calculationLink link:definitionLink 40801 - Disclosure - INTANGIBLE ASSETS, NET (Details) link:presentationLink link:calculationLink link:definitionLink 40901 - Disclosure - OTHER NON-CURRENT ASSETS (Details) link:presentationLink link:calculationLink link:definitionLink 41201 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) link:presentationLink link:calculationLink link:definitionLink 41703 - Disclosure - INCOME TAX - Reconciliation of differences between PRC statutory income tax rate and effective income tax rate (Details) link:presentationLink link:calculationLink link:definitionLink 41704 - Disclosure - INCOME TAX - Deferred income tax assets (Details) link:presentationLink link:calculationLink link:definitionLink 41705 - Disclosure - INCOME TAX - Operating loss carry forwards (Details) link:presentationLink link:calculationLink link:definitionLink 42301 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Balance Sheets (Details) link:presentationLink link:calculationLink link:definitionLink 42302 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed Statements of Results of Operations (Details) link:presentationLink link:calculationLink link:definitionLink 00090 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 00105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 00300 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) / EQUITY link:presentationLink link:calculationLink link:definitionLink 11301 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED SHARES link:presentationLink link:calculationLink link:definitionLink 31503 - Disclosure - SHARE-BASED COMPENSATION (Tables) link:presentationLink link:calculationLink link:definitionLink 40202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash (Details) link:presentationLink link:calculationLink link:definitionLink 40203 - 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Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES - Movement of provision (Details) link:presentationLink link:calculationLink link:definitionLink 41301 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED SHARES (Details) link:presentationLink link:calculationLink link:definitionLink 41302 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED SHARES - Series A Preferred Shares activities (Details) link:presentationLink link:calculationLink link:definitionLink 41401 - Disclosure - ORDINARY SHARES AND SERIES SEED PREFERRED SHARES (Details) link:presentationLink link:calculationLink link:definitionLink 41501 - Disclosure - SHARE-BASED COMPENSATION - Restricted ordinary shares (Details) link:presentationLink link:calculationLink link:definitionLink 41502 - Disclosure - SHARE-BASED COMPENSATION - Compensation expense recognized for restricted ordinary shares (Details) link:presentationLink link:calculationLink link:definitionLink 41503 - Disclosure - SHARE-BASED COMPENSATION - Transfer of ordinary shares (Details) link:presentationLink link:calculationLink link:definitionLink 41504 - Disclosure - SHARE-BASED COMPENSATION - 2016 Global Incentive Plan (Details) link:presentationLink link:calculationLink link:definitionLink 41505 - Disclosure - SHARE-BASED COMPENSATION - 2018 Share Incentive Plan (Details) link:presentationLink link:calculationLink link:definitionLink 41601 - Disclosure - FAIR VALUE MEASUREMENT - Fair value hierarchy for assets and liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 41602 - Disclosure - FAIR VALUE MEASUREMENT - Level 3 Reconciliation (Details) link:presentationLink link:calculationLink link:definitionLink 41701 - Disclosure - INCOME TAX (Details) link:presentationLink link:calculationLink link:definitionLink 41702 - Disclosure - INCOME TAX - Components of (loss)/income before income taxes and withholding tax on undistributed dividends (Details) link:presentationLink link:calculationLink link:definitionLink 41802 - Disclosure - NET LOSS PER ORDINARY SHARE - Antidilutive securities (Details) link:presentationLink link:calculationLink link:definitionLink 41901 - Disclosure - REVENUE INFORMATION - Disaggregation of revenue (Details) link:presentationLink link:calculationLink link:definitionLink 41902 - Disclosure - REVENUE INFORMATION - Revenues based on geographic areas (Details) link:presentationLink link:calculationLink link:definitionLink 42201 - Disclosure - SUBSEQUENT EVENTS (Details) link:presentationLink link:calculationLink link:definitionLink 42303 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION - Condensed statements of cash flows (Details) link:presentationLink link:calculationLink link:definitionLink 00205 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 00305 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' (DEFICIT) / EQUITY (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 00405 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 10101 - Disclosure - DESCRIPTION OF ORGANIZATION AND PRINCIPAL ACTIVITIES link:presentationLink link:calculationLink link:definitionLink 10201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES link:presentationLink link:calculationLink link:definitionLink 10301 - Disclosure - SHORT-TERM INVESTMENTS link:presentationLink link:calculationLink link:definitionLink 10401 - Disclosure - ACCOUNTS RECEIVABLES, NET link:presentationLink link:calculationLink link:definitionLink 10501 - Disclosure - INVENTORIES link:presentationLink link:calculationLink link:definitionLink 10601 - Disclosure - PREPAYMENTS AND OTHER CURRENT ASSETS link:presentationLink link:calculationLink link:definitionLink 10701 - Disclosure - PROPERTY AND EQUIPMENT, NET link:presentationLink link:calculationLink link:definitionLink 10801 - Disclosure - INTANGIBLE ASSETS, NET link:presentationLink link:calculationLink link:definitionLink 10901 - Disclosure - OTHER NON-CURRENT ASSETS link:presentationLink link:calculationLink link:definitionLink 11001 - Disclosure - SHORT-TERM BANK BORROWINGS AND RESTRICTED CASH link:presentationLink link:calculationLink link:definitionLink 11101 - Disclosure - CONVERTIBLE LOAN link:presentationLink link:calculationLink link:definitionLink 11201 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES link:presentationLink link:calculationLink link:definitionLink 11401 - Disclosure - ORDINARY SHARES AND SERIES SEED PREFERRED SHARES link:presentationLink link:calculationLink link:definitionLink 11501 - Disclosure - SHARE-BASED COMPENSATION link:presentationLink link:calculationLink link:definitionLink 11601 - Disclosure - FAIR VALUE MEASUREMENT link:presentationLink link:calculationLink link:definitionLink 11701 - Disclosure - INCOME TAX link:presentationLink link:calculationLink link:definitionLink 11801 - Disclosure - NET LOSS PER ORDINARY SHARE link:presentationLink link:calculationLink link:definitionLink 11901 - Disclosure - REVENUE INFORMATION link:presentationLink link:calculationLink link:definitionLink 12001 - Disclosure - COMMITMENTS AND CONTINGENCIES link:presentationLink link:calculationLink link:definitionLink 12101 - Disclosure - RELATED PARTY TRANSACTIONS link:presentationLink link:calculationLink link:definitionLink 12201 - Disclosure - SUBSEQUENT EVENTS link:presentationLink link:calculationLink link:definitionLink 12301 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION link:presentationLink link:calculationLink link:definitionLink 20202 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies) link:presentationLink link:calculationLink link:definitionLink 30103 - Disclosure - DESCRIPTION OF ORGANIZATION AND PRINCIPAL ACTIVITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 30203 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables) link:presentationLink link:calculationLink link:definitionLink 30303 - Disclosure - SHORT-TERM INVESTMENTS (Tables) link:presentationLink link:calculationLink link:definitionLink 30403 - Disclosure - ACCOUNTS RECEIVABLES, NET (Tables) link:presentationLink link:calculationLink link:definitionLink 30503 - Disclosure - INVENTORIES (Tables) link:presentationLink link:calculationLink link:definitionLink 30603 - Disclosure - PREPAYMENTS AND OTHER CURRENT ASSETS (Tables) link:presentationLink link:calculationLink link:definitionLink 30703 - Disclosure - PROPERTY AND EQUIPMENT, NET (Tables) link:presentationLink link:calculationLink link:definitionLink 30803 - Disclosure - INTANGIBLE ASSETS, NET (Tables) link:presentationLink link:calculationLink link:definitionLink 30903 - Disclosure - OTHER NON-CURRENT ASSETS (Tables) link:presentationLink link:calculationLink link:definitionLink 31003 - Disclosure - SHORT-TERM BANK BORROWINGS AND RESTRICTED CASH (Tables) link:presentationLink link:calculationLink link:definitionLink 31203 - Disclosure - ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables) link:presentationLink link:calculationLink link:definitionLink 31303 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED SHARES (Tables) link:presentationLink link:calculationLink link:definitionLink 31603 - Disclosure - FAIR VALUE MEASUREMENT (Tables) link:presentationLink link:calculationLink link:definitionLink 31703 - Disclosure - INCOME TAX (Tables) link:presentationLink link:calculationLink link:definitionLink 31803 - Disclosure - NET LOSS PER ORDINARY SHARE (Tables) link:presentationLink link:calculationLink link:definitionLink 31903 - Disclosure - REVENUE INFORMATION (Tables) link:presentationLink link:calculationLink link:definitionLink 32003 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables) link:presentationLink link:calculationLink link:definitionLink 32303 - Disclosure - PARENT COMPANY ONLY CONDENSED FINANCIAL INFORMATION (Tables) link:presentationLink link:calculationLink link:definitionLink 40101 - Disclosure - DESCRIPTION OF ORGANIZATION AND PRINCIPAL ACTIVITIES - Principal terms of VIE Agreements (Details) link:presentationLink link:calculationLink link:definitionLink 40201 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) link:presentationLink link:calculationLink link:definitionLink 40204 - 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Disclosure - INCOME TAX - PRC Tax Administration and Collection Law (Details) link:presentationLink link:calculationLink link:definitionLink 41801 - Disclosure - NET LOSS PER ORDINARY SHARE - Basic and diluted net loss per share computation (Details) link:presentationLink link:calculationLink link:definitionLink 42001 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details) link:presentationLink link:calculationLink link:definitionLink