SEGMENTS - Reportable Segment Performance (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021		Jun. 30, 2022	Jun. 30, 2021		Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenue	$ 80,553	$ 63,129	[1]	$ 232,612	$ 156,947	[1]
Other costs of services	(19,749)	(16,064)	[1]	(52,890)	(41,044)	[1]
Residuals	10,657	8,128		27,666	20,424
Processing margin	71,461	55,193		207,388	136,327
Selling, general and administrative	(47,775)	(37,296)	[1]	(142,878)	(92,769)	[1]
Depreciation and amortization	(7,506)	(6,995)	[1]	(21,823)	(17,938)	[1],[2],[3]
Change in fair value of contingent consideration	(8,254)	(3,609)	[1]	(24,684)	(5,835)	[1],[2],[3]
Loss from operations	(2,731)	(835)	[1]	(9,663)	(639)	[1]
Total assets	780,424	648,251		780,424	648,251		$ 651,800
Goodwill	353,882	289,046		353,882	289,046		292,243
Merchant Services
Segment Reporting Information [Line Items]
Revenue	32,714	29,963		91,071	81,130
Other costs of services	(16,303)	(14,206)		(43,273)	(36,829)
Residuals	10,320	8,374		26,555	21,219
Processing margin	26,731	24,131		74,353	65,520
Total assets	204,656	209,989		204,656	209,989
Goodwill	119,086	119,086		119,086	119,086		119,086
Proprietary Software and Payments
Segment Reporting Information [Line Items]
Revenue	47,839	33,729		141,575	77,491
Other costs of services	(3,456)	(2,397)		(9,660)	(5,864)
Residuals	348	273		1,139	817
Processing margin	44,731	31,605		133,054	72,444
Total assets	510,336	377,416		510,336	377,416
Goodwill	234,796	169,960		234,796	169,960		173,157
Other
Segment Reporting Information [Line Items]
Revenue	0	(563)		(34)	(1,674)
Other costs of services	10	539		43	1,649
Residuals	(11)	(519)		(28)	(1,612)
Processing margin	(1)	(543)		(19)	(1,637)
Total assets	65,432	60,846		65,432	60,846
Goodwill	$ 0	$ 0		$ 0	$ 0		$ 0

[1] Effective October 1, 2020, the Company's financial statements are presented in accordance with ASU 2021-08, Accounting Standards Codification Topic 805, Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. See Note 2 to the interim consolidated financial statements for a description of the recently adopted accounting pronouncement and the impacts of adoption on the condensed consolidated statements of operations.

[2] Effective October 1, 2020, the Company's financial statements are presented in accordance with ASU 2021-08, Accounting Standards Codification Topic 805, Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. See Note 2 to the interim consolidated financial statements for a description of the recently adopted accounting pronouncement and the impacts of adoption on the condensed consolidated statements of cash flows.

[3] The prior period amounts included in the statement of cash flows have been updated to correct settlement assets as restricted cash, which were previously reported as cash flows used in operating and investing activities. These adjustments reflect a decrease in prior year cash flows provided by operating activities of $2,046 and a decrease of $7,009 in cash outflows for acquisitions of businesses, net of cash and restricted cash acquired within cash flows used in investing activities, resulting in a combined increase of $4,963 in cash, cash equivalents, and restricted cash at the end of the period.