REVENUE - Schedule of Revenue by (Details) - USD ($) $ in Thousands	3 Months Ended					12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue	$ 45,780	$ 49,017	$ 42,760	$ 38,285	$ 36,877	$ 166,939
Subscription and transaction fees
Disaggregation of Revenue [Line Items]
Revenue	40,625	38,234	34,686	33,214	33,108	139,242
Transaction fees
Disaggregation of Revenue [Line Items]
Revenue	26,421	24,365	21,002	20,454	19,677	85,498
Subscription fees
Disaggregation of Revenue [Line Items]
Revenue	14,204	13,869	13,684	12,760	13,431	53,744
Equipment sales
Disaggregation of Revenue [Line Items]
Revenue	$ 5,155	$ 10,783	$ 8,074	$ 5,071	$ 3,769	$ 27,697