STOCKHOLDERS’ EQUITY (DEFICIT) - Common Stock Reserved for Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	176,758,741	1,039,908,056
Convertible preferred stock (on an as-converted basis)
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	0	957,159,704
Convertible preferred stock warrant (on an as-converted basis)
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	0	1,546,799
Private warrants to purchase common stock
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	44,350,000	0
Public warrants to purchase common stock
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	9,317,468	0
Stock options outstanding
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	67,013,622	70,675,318
RSUs
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	43,183,277	0
Shares available for future grants under equity plans
Class of Stock [Line Items]
Common shares reserved for future issuance (in shares)	12,894,374	10,526,235