Post raw JSON using Retrofit 2

I have a big JSON object received from another application and I have to make a post call to an API using Retrofit 2.
All the examples or topics that I find on this topic use an JSONObject or a Map. That means I have to parse my string (JSON) in order to create the JSONObject or Map.

But I want to put directly my string in the body somehow.

I tried this way, but it doesn't work:

@Headers("Content-Type: application/json")
@POST("transactions")
Call<Void> submitTransaction(@Body String body);

This way I am sending a string that is escaped as a body and my JSON looks strange:
screenshot

You need to add a Scalars Converter to the list of your Gradle dependencies, which would take care of converting java.lang.String objects to text/plain request bodies, beacause Retrofit uses Gson converter by default. Check this link for the latest version.

https://search.maven.org/search?q=g:com.squareup.retrofit2%20a:converter-scalars

dependencies {
    implementation “com.squareup.retrofit2:converter-scalars:2.4.0”
    ..
}

Then, you need to pass a correct converter factory to your Retrofit builder. It will later tell Retrofit how to convert the @Body parameter passed to the service.

val retrofit = Retrofit.Builder()
        .client(okHttpClient)
        .baseUrl("/")
        .addConverterFactory(ScalarsConverterFactory.create())
        .build()

After this, it is time for setting up a Retrofit service with a String body parameter.

@Headers("Content-Type: application/json")
@POST("transactions")
Call<Void> submitTransaction(@Body String body);