| Share-based compensation - Options (Details) - $ / shares | 3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | |
| Share-based compensation | ||||
| Number of options over ordinary shares granted (in shares) | 1,795,872 | 30,247,398 | 43,982,424 | 52,002,726 | 
| Weighted average fair value of ordinary shares options (in dollars per share) | $ 0.19 | $ 0.05 | $ 0.12 | $ 0.08 | 
| Number of additional options with a nominal exercise price granted | 2,540,640 | 6,148,186 | 30,655,824 | 26,015,098 | 
| Weighted average fair value of options with a nominal exercise price | $ 0.24 | $ 0.15 | $ 0.15 | $ 0.17 | 
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. No definition available. 
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- Definition Gross number of share options (or share units) granted with nominal exercise price during the period. No definition available. 
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- References No definition available. 
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- Definition Gross number of share options (or share units) granted during the period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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