Segment reporting - Geographic information (Details) - EUR (€) € in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of operating segments [line items]
Revenue	€ 8,275	€ 41,353	€ 40,366
Non-current assets	12,969	4,442	18,741
Germany
Disclosure of operating segments [line items]
Revenue	5	152	742
Non-current assets	12,969	3,435	4,896
Czech Republic
Disclosure of operating segments [line items]
Non-current assets	0	1,007	1,306
USA
Disclosure of operating segments [line items]
Revenue	8,270	41,201	39,624
Non-current assets	€ 0	€ 0	€ 12,539

The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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+ Details