Fair value measurements - Valuation of Derivative Liability (Details)	Sep. 30, 2024 Y	Sep. 30, 2023 Y
Expected term | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.2	0.0
Expected term | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.4	0.4
Volatility | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.551	0.432
Volatility | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.599	0.832
Risk-free interest rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.054	0.052
Risk-free interest rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.055	0.056
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.0	0.0
Probability of option exercise | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	0.000	0.300
Probability of option exercise | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Liability measurement input	1.000	1.000