Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

There is an issue with deserializing DateOnly properties with generated DateOnlyJsonConverter deserialization fail with

System.NotSupportedException: Specified method is not supported.
at DateOnlyJsonConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)

openapi-generator version

7.16.0

OpenAPI declaration file content or url

Schema

Generation Details

Steps to reproduce

• Use schema above
• generate client
• Try to deserialize json

{"id":1,"created":"2025-10-07"}

Related issues/PRs

Suggest a fix

If you want to parse DateOnly type you cannot provide settings for Time with DateTimeStyles enum.

TryParse should be like this

if (DateOnly.TryParseExact(value, format, CultureInfo.InvariantCulture, DateTimeStyles.None, out DateOnly result))
return result;