JsonSyntaxException：IllegalStateException：预期BEGIN_OBJECT但是为STRING

Question

从外部源获取JSON并尝试使用GSON解析它，我得到了上面提到的错误。这是我的主要活动：

final ProgressDialog dialog;

        dialog = new ProgressDialog(PlayerDetailsActivity.this);
        dialog.setTitle(getString(R.string.string_getting_json_title));
        dialog.setMessage(getString(R.string.string_getting_json_message));
        dialog.show();

        ApiService api = RetroClient.getApiService();

        Call<PlayerRolesList> call = api.getMyJSON();

        call.enqueue(new Callback<PlayerRolesList>() {
            @Override
            public void onResponse(Call<PlayerRolesList> call, Response<PlayerRolesList> response) {
                //Dismiss Dialog
                dialog.dismiss();

                if(response.isSuccessful()) {
                    /**
                     * Got Successfully
                     */
                    Toast.makeText(PlayerDetailsActivity.this, "Successful", Toast.LENGTH_LONG).show();
                    alPlayerRoles = response.body().getPlayerRoles();

                    /**
                     * Binding that List to Adapter
                     */
                    adapter = new PlayerDetailsAdapter(PlayerDetailsActivity.this, alPlayerRoles);
                    lvPlayerRoles.setAdapter(adapter);

                } else {
                    Toast.makeText(PlayerDetailsActivity.this, response.message(), Toast.LENGTH_LONG).show();
                }
            }

这是发出请求的代码，并且应该使用适配器填充布局。

这也是模型类：

public class PlayerRolesList {

    @SerializedName("data")
    @Expose
    private ArrayList<PlayerRolesModel> players = new ArrayList<>();

    /**
     * @return The contacts
     */
    public ArrayList<PlayerRolesModel> getPlayerRoles() {
        return players;
    }

    /**
     * @param players The player roles
     */
    public void setPlayerRoles(ArrayList<PlayerRolesModel> players) {
        this.players = players;
    }
}

我根据本教程http://www.pratikbutani.com/2016/05/android-tutorial-json-parsing-using-retrofit-part-1/

完成了整个过程

运行他的应用程序工作正常，但由于某些原因我的似乎不同意JSON，我不确定我在哪里犯错误。

此错误消息的常见原因是什么？