Retrofit call returning 400, cURL request working perfectly fine, syntax issue

[snailmail123]

I've tried making a retrofit call to an API endpoint, but it's returning a 400 error, however my curl request is working perfectly fine. I can't seem to spot the error, could someone double check my work to see where I made a mistake?

The curl call that works:

curl --request POST https://connect.squareupsandbox.com/v2/payments \
    --header "Content-Type: application/json" \
    --header "Authorization: Bearer accesstoken112233" \
    --header "Accept: application/json" \
    --data '{
    "idempotency_key": "ab2a118d-53e2-47c6-88e2-8c48cb09bf9b",
    "amount_money": {
    "amount": 100,
    "currency": "USD"},
    "source_id": "cnon:CBASEITjGLBON1y5od2lsdxSPxQ"}'

My Retrofit call:

public interface IMakePayment {

        @Headers({
                "Accept: application/json",
                "Content-Type: application/json",
                "Authorization: Bearer accesstoken112233"
        })
        @POST(".")
        Call<Void> listRepos(@Body DataDto dataDto);
    }

Retrofit Instance:

public class RetrofitClientInstance {

    private static Retrofit retrofit;
    private static final String BASE_URL = "https://connect.squareupsandbox.com/v2/payments/";


    public static Retrofit getRetrofitInstance() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}

public class Amount_money
{
    private String amount;

    private String currency;

    public String getAmount ()
    {
        return amount;
    }

    public void setAmount (String amount)
    {
        this.amount = amount;
    }

    public String getCurrency ()
    {
        return currency;
    }

    public void setCurrency (String currency)
    {
        this.currency = currency;
    }

    @Override
    public String toString()
    {
        return "ClassPojo [amount = "+amount+", currency = "+currency+"]";
    }
}

public class DataDto
{
    private String idempotency_key;

    private Amount_money amount_money;

    private String source_id;

    public String getIdempotency_key ()
    {
        return idempotency_key;
    }

    public void setIdempotency_key (String idempotency_key)
    {
        this.idempotency_key = idempotency_key;
    }

    public Amount_money getAmount_money ()
    {
        return amount_money;
    }

    public void setAmount_money (Amount_money amount_money)
    {
        this.amount_money = amount_money;
    }

    public String getSource_id ()
    {
        return source_id;
    }

    public void setSource_id (String source_id)
    {
        this.source_id = source_id;
    }

    @Override
    public String toString()
    {
        return "ClassPojo [idempotency_key = "+idempotency_key+", amount_money = "+amount_money+", source_id = "+source_id+"]";
    }
}

Making the retrofit call:

Amount_money am = new Amount_money();
        am.setAmount("100");
        am.setCurrency("USD");

        DataDto dto = new DataDto();
        dto.setIdempotency_key("55cab2a7-4d78-411b-b56d-e050864febbd");
        dto.setSource_id("cnon:CBASEPELexeldhFUrzi9u68o1ng");
        dto.setAmount_money(am);


        RetrofitInterfaces.IMakePayment service = RetrofitClientInstance.getRetrofitInstance().create(RetrofitInterfaces.IMakePayment.class);
        Call<Void> call = service.listRepos(dto);
        call.enqueue(new Callback<Void>() {
            @Override
            public void onResponse(@NonNull Call<Void> call, @NonNull Response<Void> response) {
                Log.d(TAG, "onResponse: " + response.toString());
            }

            @Override
            public void onFailure(@NonNull Call<Void> call, @NonNull Throwable t) {
                Log.d(TAG, "onFailure: Error: " + t);
            }
        });