可以先确认发送请求时的数据格式和请求头是否正确，如果数据格式不对或者请求头缺失可能导致API返回400错误。

示例代码如下：

public static String httpRequest(String url, String method, String params) {
    URL obj;
    HttpURLConnection con;
    BufferedReader in;
    StringBuffer response = new StringBuffer();
    try {
        obj = new URL(url);
        con = (HttpURLConnection) obj.openConnection();
        con.setRequestMethod(method);
        con.setRequestProperty("Content-Type", "application/json");
        con.setRequestProperty("User-Agent", "Mozilla/5.0");
        con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");
        con.setDoOutput(true);
        if (params != null) {
            OutputStream os = con.getOutputStream();
            os.write(params.getBytes("UTF-8"));
            os.flush();
            os.close();
        }
        int responseCode = con.getResponseCode();
        if (responseCode == HttpURLConnection.HTTP_OK) {
            in = new BufferedReader(new InputStreamReader(con.getInputStream()));
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();
        } else {
            response.append("{\"status\":\"error\",\"message\":\"" +
                    "HTTP Error Code: " + responseCode + "\"}");
        }
    } catch (IOException e) {
        e.printStackTrace();
        response.delete(0, response.length());
        response.append("{\"status\":\"error\",\"message\":\"" +
                "IOException: " + e.getMessage() + "\"}");
    }
    return response.toString();
}

在使用此方法发送请求时，需要确保传入的数据格式是符合API要求的，例如JSON格式、XML格式等。同时，可以根据API的要求修改请求头中的属性，例如Accept、Authorization等。