Retrofit: Unable to create @Body converter for class

You can specify a Converter when you create the Retrofit like this

Retrofit retrofit = new Retrofit.Builder()
        .addConverterFactory(GsonConverterFactory.create())
        .baseUrl(baseurl)
        .client(okHttpClient)
        .build();

there is chance of you kept same @SerializedName("") for multiple vairable/fields/tags

Solution: declare body value in your interface with next:

@Body RequestBody body and wrap String JSON object:

RequestBody body = RequestBody.create(MediaType.parse("application/json"), obj.toString());