We have begun implementing Sign in with Apple in our mobile app but cannot seem to call the token endpoint successfully (https://appleid.apple.com/auth/token). The response we get is 400 with the body [{"error":"invalid_client"}]. I have read and re-read the details on how to generate the client-secret. We are using a java backend and specifically the nimbus library to create the signed JWT.final JWSHeader clientSecretHeader = new JWSHeader.Builder(JWSAlgorithm.ES256) .keyID("7N5XJ*****") .build(); final Date issuedAtTime = Date.from(Instant.now()); final Date expirationTime = Date.from(Instant.now().plusSeconds(3600)); final JWTClaimsSet clientSecretClaims = new JWTClaimsSet.Builder() .issuer("HL46P*****") .issueTime(issuedAtTime) .expirationTime(expirationTime) .audience("https://appleid.apple.com") .subject("com.company.app") .build(); final ECPrivateKey signingKey = ...private key loaded from p8 file...; final JWSSigner jwtSigner = new ECDSASigner(signingKey); final SignedJWT clientSecretJwt = new SignedJWT(clientSecretHeader, clientSecretClaims); clientSecretJwt.sign(jwtSigner); MultiValueMap<string, string=""> map= new LinkedMultiValueMap<>(); map.add("grant_type", "authorization_code"); map.add("client_id", "HL46P*****"); map.add("client_secret", clientSecretJwt.serialize()); map.add("code", "code receiged from app..."); final HttpEntity<multivaluemap<string, string="">> request = new HttpEntity<>(map); final RestTemplate restTemplate = new RestTemplateBuilder().build(); final ResponseEntity response = response = restTemplate.postForEntity( "https://appleid.apple.com/auth/token", request, GetTokenResponse.class );The resulting JWT looks like the following:Header{ "kid": "7N5XJ*****", "alg": "ES256" }Claims{ "aud": "https://appleid.apple.com", "sub": "com.company.app", "iss": "HL46P.....", "exp": 1585583898, "iat": 1585580298 }I am out of ideas on what we are doing wrong.