问腾讯会议API 签名，为何报签名失败？

Mac hmacSha256 = Mac.getInstance("HmacSHA256");
byte[] keyBytes = secret.getBytes("UTF-8");
hmacSha256.init(new SecretKeySpec(keyBytes, 0, keyBytes.length, "HmacSHA256"));
String hexString = byteArrayToHex(stringToSign.getBytes("UTF8"));
String sign = new String(Base64.encodeBase64(hmacSha256.doFinal(hexString),"UTF-8"));

const secretId = 'xxx';
const secretKey = 'xxx';
const params = {
      userid: 'xx',
      instanceid: 1,
      subject: subject,
      type: 0,
      start_time: getTime(startTime),
      end_time: getTime(endTime),
      settings: {}
};

const HTTPMethod = 'POST';
const url = '/v1/meetings';

const headerString = 'X-TC-Key=' + secretId + '&X-TC-Nonce=' + randomNumber(10000, 99999) + '&X-TC-Timestamp=' + nowTime();
const stringToSign = HTTPMethod + '\n' +
      headerString + '\n' +
      url + '\n' +
      JSON.stringify(params);
console.log(stringToSign);
const key = CryptoJS.enc.Utf8.parse(secretKey);
const content = CryptoJS.enc.Utf8.parse(stringToSign);
const hmac = CryptoJS.enc.Hex.stringify(CryptoJS.HmacSHA256(content, key));
console.log(btoa(hmac));

import java.nio.charset.StandardCharsets;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
public class test{
     public static void main(String []args) throws NoSuchAlgorithmException, InvalidKeyException{
        String headerString = "X-TC-Key=xxx&X-TC-Nonce=84578&X-TC-Timestamp=1586765524";
        String HTTPMethod = "GET";
        String requestUri = "https://api.meeting.qq.com/v1/meetings?userid=xxx&instanceid=1";
        String stringToSign = HTTPMethod + "\n" + headerString  + "\n" + requestUri + "\n" + "";
        System.out.println(stringToSign);                      
        String secretKey = "xxx";
        Mac mac = Mac.getInstance("HmacSHA256");
        SecretKeySpec secretKeySpec = new SecretKeySpec(secretKey.getBytes(StandardCharsets.UTF_8), mac.getAlgorithm());
        System.out.println(secretKeySpec);
        mac.init(secretKeySpec);
        byte[] hash = mac.doFinal(stringToSign.getBytes(StandardCharsets.UTF_8));
        System.out.println(hash);   
        char[] buf = new char[hash.length * 2];
        char[] HEX_CHAR = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        int index = 0;
        for (byte b : hash) {
          buf[index++] = HEX_CHAR[b >>> 4 & 0xf];
          buf[index++] = HEX_CHAR[b & 0xf];
        }
  
        String hexHash = new String(buf);
        System.out.println(hexHash);
        System.out.println(new String(Base64.getEncoder().encode(hexHash.getBytes(StandardCharsets.UTF_8))));
     }
}