This is on ktor 1.6.0, coroutines 1.5.0-native-mt and serialization 1.2.1, it was working perfectly with ktor 1.4.0 / coroutine 1.4.2-native-mt / serialization 1.0.0-RC The call is the following:

<http://httpClient.post|httpClient.post><LoginResponse> {
            url { encodedPath = LOGIN_WITH_INIT_URL }
            body = TokenGenerationInput(username, password)
        }

Any ideas on what's happening here?

It might be serialization 1.2.1 causing the issue. I had a similar error. Adding useAlternativeNames = false to the Json config worked around for me.

I have the same issue with kotlinx.serialization 1.1.0 and kotlin 1.5.x. Will try the workaround, thanks!

yup, helped me as well

setting

useAlternativeNames = false

worked! thanks!