Registration of securities issued in business combination transactions

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Basic and diluted net income per share calculation (FY) (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Basic and diluted net income per share calculation (FY) (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Sep. 30, 2020
Jun. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Common stock subject to possible redemption                  
Interest earned on marketable securities held in Trust Account   $ (3,473)     $ (6,646)   $ (10,306) $ (6,646) $ (11,254)
Non-Redeemable Common Stock                  
Net loss $ (1,000) $ 724,257 $ (4,669,435) $ 4,641,710 $ (453,098) $ 0 $ 696,532 $ (453,098) (2,061,769)
Common Class Subject To Redemption [Member]                  
Common stock subject to possible redemption                  
Less: Income taxes and franchise fees                 $ (11,254)
Weighted average shares outstanding, basic                 21,833,901
Weighted average shares outstanding, diluted                 21,833,901
Basic net income per common share                 $ 0.00
Diluted net income per common share                 $ 0.00
Non-Redeemable Common Stock                  
Weighted average shares outstanding, basic                 21,833,901
Weighted average shares outstanding, diluted                 21,833,901
Basic net income per common share                 $ 0.00
Diluted net income per common share                 $ 0.00
Common Class Not Subject To Redemption [Member]                  
Common stock subject to possible redemption                  
Weighted average shares outstanding, basic                 2,318,726
Weighted average shares outstanding, diluted                 2,318,726
Basic net income per common share $ 0.00               $ (0.89)
Diluted net income per common share $ 0.00               $ (0.89)
Non-Redeemable Common Stock                  
Net loss $ (1,000)               $ (2,061,769)
Non-Redeemable Net loss $ (1,000)               $ (2,061,769)
Weighted average shares outstanding, basic                 2,318,726
Weighted average shares outstanding, diluted                 2,318,726
Basic net income per common share $ 0.00               $ (0.89)
Diluted net income per common share $ 0.00               $ (0.89)