Significant accounting policies - Concentration and risk (Details)	12 Months Ended
Dec. 31, 2023 Distributor customer	Dec. 31, 2022 Distributor	Dec. 31, 2021 Distributor item
Revenue \| Customer concentration \| Offline distributor A
Significant accounting policies
Number of distributor	1	1	1
Accounts and notes receivable \| Credit concentration \| Offline distributor
Significant accounting policies
Number of distributor		2	2
Number of customer \| customer	4
Total concentration risk	61.00%	33.00%	28.00%
Purchases \| Supplier concentration \| One supplier A
Significant accounting policies
Number of suppliers \| item			1
Total concentration risk	58.00%	80.00%	75.00%
Accounts and notes payable due \| Supplier concentration \| One supplier A
Significant accounting policies
Total concentration risk	74.00%	86.00%	89.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482861/275-10-50-18

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482861/275-10-50-20

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration