Unable to create converter for class com.anyarscaner.model.ResponModel

Question

I created the Retrofit API function, but it's an obstacle like the following. I corrected it yesterday, but after today it returned to the same problem. Here's the Error.

Unable to create converter for class com.anyarscaner.model.ResponModel

here's my API code

ApiConfig.instanceRetrofit.totalPoin(tv_nama.text.toString()).enqueue(object : Callback<ResponModel>{
            override fun onResponse(call: Call<ResponModel>, response: Response<ResponModel>) {
                val respon = response.body()!!
                s.setString(s.total_poin, respon.total_poin).toString()

                pbPoin.visibility = View.GONE

                if (respon.success == 1) {
                    val getPoin = s.getString(s.total_poin)
                    tv_poin.text = getPoin
                }
            }

            override fun onFailure(call: Call<ResponModel>, t: Throwable) {
                Toast.makeText(activity, "Terjadi Kesalahan: "+t.message, Toast.LENGTH_SHORT).show()
            }

        })

here's my Model Response class

class ResponModel {
    var success = 1
    var error = 0
    lateinit var message:String
    lateinit var total_poin: String
}

can anyone help me?