Implementation

Map<String, Object> data = new HashMap<>();
data.put("appId", "appid");
data.put("amount", "100");
data.put("callbackURL", "https://your.callback.url");
data.put("saleNumber", "");
data.put("remark", "this is remark");
Gson gson = new Gson();
RequestBody body = RequestBody.create(gson.toJson(data), MediaType.parse("application/json; charset=utf-8"));
String token = "eyJhbGciOiJIUzUxMiJ9.eyJzdWIiOiJPTjAwMDAwMDk3MTMwIiwiYXVkaWVuY2UiOm51bGwsInJvbGUiOm51bGwsImNyZWF0ZWQiOjE2NzgyMTU4MDU2NjYsInVzZXJ0eXBlIjoiQ1VTVE9NRVIiLCJleHAiOjE2NzgyMjQ4MDUsInVzZXJpZCI6MTMwfQ.WVpasVp958R6kHOcqC3QgQjCqTXIkyagutkONxCV97yT_hmp9Q6WaZ921cjxhzJA4v2Bhd0RTF5QHMLddVnzOQ";
Request request = new Request.Builder()
        .url("https://ecom-api.ottpay.com/api/v1/pay/weixin/inapp-pay")
        .addHeader("Authorization", "Bearer " + token)
        .post(body)
        .build();
final OkHttpClient httpClient = new OkHttpClient();
try (Response response = httpClient.newCall(request).execute()) {
    if (!response.isSuccessful()) {
        System.out.println(response.body().string());
        throw new IOException("Unexpected code " + response);
    }
    // Response
    System.out.println(response.body().string());
} catch (IOException e) {
    throw new RuntimeException(e);
}