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Stock-based compensation - Common stock warrants (Details) - $ / shares
Dec. 31, 2021
Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Balance (in usd per share) $ 0.81  
Balance (in usd per share) $ 0.81 $ 0.81
Balance (in shares) 12,654,807  
Balance (in shares) 16,336,134 12,654,807
Common Stock Warrants [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Balance (in usd per share)   $ 1.75
Balance (in usd per share) $ 1.75  
Balance (in shares) 617,972  
Balance (in shares) 617,972 617,972
Preferred Stock Warrants [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Balance (in usd per share)   $ 1.92
Balance (in usd per share) $ 1.92  
Balance (in shares) 3,247,637  
Balance (in shares) 3,247,637 3,247,637