I want to debug HttpException

Question

"is not a valid element" Gives a fault

If the server is down when I log in to the application, an error message should normally be written and the response value returns 500.

AppApi.kt

@POST(Constants.LOGIN_ENDPOINT)
@Headers("No-Authentication: true")
fun requestLogin(@Body loginModel: LoginModel): Observable<LoginResponse>

LoginRepository.kt

 fun requestLogin(loginModel: LoginModel): Observable<LoginResponse> {
        return appApi.requestLogin(loginModel)
    }

LoginViewModel.kt

fun requestLogin(loginModel: LoginModel): MutableLiveData<ResponseControl<LoginResponse?>> {
    loginRepository.requestLogin(loginModel).subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread()).subscribe({
            requestLoginMutableLiveData.postValue(ResponseControl.Success(it))
        }, {
            sendError(
                ErrorModel(
                    exceptionMessage = it.localizedMessage,
                    innerExceptionStackTrace = it.stackTraceToString()
                )
            )
            //but it doesn't come here
            if (it is HttpException) {
                if (it.code() == 401) {
                    requestLoginMutableLiveData.postValue(ResponseControl.AuthorizationError())
                } else {
                    val errorMessage = it.response()?.errorBody()?.string()
                    val errorDetail = Gson().fromJson(errorMessage, ApiError::class.java)
                    requestLoginMutableLiveData.postValue(
                        ResponseControl.Error(
                            message = errorDetail.message,
                            data = null
                        )
                    )
                }
            } else {
                requestLoginMutableLiveData.postValue(
                    ResponseControl.Error(
                        null,null
                    )
                )
            }

        }).let {
            compositeDisposable.add(it)
        }

    return requestLoginMutableLiveData
}

//LoginActivity

viewModel.requestLoginMutableLiveData.observe(this) { response ->
            when (response) {
                is ResponseControl.Success -> {
                    //Login is Success
                    saveTokens(response.data!!)
                }

                is ResponseControl.Error -> {
                    if (response.message.isNullOrEmpty()) {
                        showError(getString(R.string.an_error_occured))
                    } else {
                        showError(getStringWithKey(response.message))
                    }
                    binding.loginButton.text = getString(R.string.login)
                    binding.buttonProgressBar.gone()
                    binding.loginButton.isClickable = true
                }

                else -> {}
            }
        }

Is there any wrong part in my code? Can you please correct it?