bad request error when authenticating using https://ims-na1.adobelogin.com:443/ims/exchange/jwt

package io.adobe.solutions;

import static java.lang.Boolean.TRUE;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

public class IMSClient {

public static String getJWTToken(String orgId, String technicalAccountId, String apiKey,String keyPath,String imsHost, String[] metascopes, int requestedExpirationTime)
throws NoSuchAlgorithmException, InvalidKeySpecException, IOException {
// Expiration time in seconds
Long expirationTime = System.currentTimeMillis() / 1000 + requestedExpirationTime;
// Metascopes associated to key
//String metascopes[] = metascopes;

// # create the certificate and private key using openssl
// $ openssl req -nodes -text -x509 -newkey rsa:2048 -keyout secret.pem -out
// certificate.pem -days 356
//
// Upload the certificate.pem in Adobe IO Console-> Your Integration-> Public
// keys
//
// # convert private key to DER format
// $ openssl pkcs8 -topk8 -inform PEM -outform DER -in secret.pem -nocrypt >
// secret.key

// Secret key as byte array. Secret key file should be in DER encoded format.
byte[] privateKeyFileContent = Files.readAllBytes(Paths.get(keyPath));

// Read the private key
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
KeySpec ks = new PKCS8EncodedKeySpec(privateKeyFileContent);
RSAPrivateKey privateKey = (RSAPrivateKey) keyFactory.generatePrivate(ks);

// Create JWT payload
Map<String, Object> jwtClaims = new HashMap<String, Object>();
jwtClaims.put("iss", orgId);
jwtClaims.put("sub", technicalAccountId);
jwtClaims.put("exp", expirationTime);
jwtClaims.put("aud", "https://" + imsHost + "/c/" + apiKey);
for(String metascope : metascopes) {
jwtClaims.put("https://" + imsHost + "/s/" + metascope, TRUE);
}

SignatureAlgorithm sa = SignatureAlgorithm.RS256;
// Create the final JWT token
String jwtToken = Jwts.builder().setClaims(jwtClaims).signWith(sa, privateKey).compact();

return jwtToken;
}

}

As i said, the issue happens from time to time and we are using the same parameters.

Any ideas how to fix this?

Thanks