Ktor POST body params not sent

I have a post request done with Ktor this way

val response = httpClient.post("${BASE_URL}/following") {
   contentType(ContentType.Application.Json)
   setBody(UnfollowRequestBody(userId, "delete"))
}

With the class being

@Serializable
data class UnfollowRequestBody(
    @SerialName("user_id") val userId: Int?,
    @SerialName("_method") val method: String = "delete",
)

When this call is logged

METHOD: POST
BODY Content-Type: application/json
BODY START
{"user_id":28367}
BODY END

the second parameter is omitted, which causes an API error as without the _method being set to "delete" it treats the request as a follow request, instead of an unfollow one.

Any idea on how to force the second parameter to be sent as well?

I found the answer. By default, Ktor doesn't encode default parameters.

So, for this, there are 2 possible solutions:

1. add encodeDefaults = true in the Ktor client configuration

2. Remove the = "delete" from the data class definition