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Some useful links to gather information about your Nextcloud Talk installation:
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Elasticsearch 8.19.8 rejects the Accept: application/vnd.elasticsearch+json; compatible-with=9 header, returning HTTP 400 even for simple GET / requests.
As long as the Nextcloud Full Text Search – Elasticsearch app sends this header, it will never work.
Conclusion
This is a hard incompatibility between:
-
Nextcloud 32 (Hub 25) with the
fulltextsearch_elasticsearchapp
→ uses the Elasticsearch PHP client 9.x and sends
compatible-with=9 -
Elasticsearch 8.19.8
→ does not acceptcompatible-with=9requests
Because of this mismatch, the Full Text Search platform test fails and indexing/searching cannot start, even though Elasticsearch itself is running and healthy.
Important note
This is not a problem with:
-
networking
-
Docker
-
disk space
-
permissions
-
Nextcloud configuration
It is a protocol-level compatibility issue between the client used by Nextcloud and the Elasticsearch server version.