Registration of securities issued in business combination transactions

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Q3) (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Q3) (Details) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Cash equivalents $ 0 $ 0 $ 0
Unrecognized tax benefits 0 0  
Accrued for interest and penalties amount 0 $ 0  
Shares excluded in the calculation of diluted loss per share   11,825,000  
Cash, FDIC Insured Amount $ 250,000 $ 250,000  
New Warrants      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Shares excluded in the calculation of diluted loss per share 11,825,000 11,825,000