Hello, I have implemented Sign in with Apple in my iOS app and am currently trying to implement the revocation feature. However, I keep encountering an invalid_client error when calling the Apple authentication/revocation API. Here are the details of my configuration: Team ID: HUGD2H952H Client ID: com.puppylink.puppylinkapp Key ID: KXSYK98424 I am using these details to generate a client secret with the JWT ES256 algorithm. Below is the code I am using on the backend server to generate the client secret: private fun makeClientSecret(): String { val now: ZonedDateTime = ZonedDateTime.now(ZoneOffset.UTC) val expirationTime: ZonedDateTime = now.plusMinutes(5) // Setting expiration time to 5 minutes return Jwts.builder() .setHeaderParam(JwsHeader.KEY_ID, appleProperties.keyId) .setHeaderParam("alg", "ES256") .setIssuer(appleProperties.teamId) .setIssuedAt(Date.from(now.toInstant())) .setExpiration(Date.from(expirationTime.toInstant())) .setAudience("https://appleid.apple.com") .setSubject(appleProperties.clientId) .signWith(getPrivateKey(), SignatureAlgorithm.ES256) .compact() } private fun getPrivateKey(): PrivateKey { val resource = ClassPathResource(appleProperties.privateKeyFile) val privateKey = String(Files.readAllBytes(Paths.get(resource.uri))) val pemReader: Reader = StringReader(privateKey) val pemParser = PEMParser(pemReader) val converter = JcaPEMKeyConverter() val keyInfo = pemParser.readObject() as PrivateKeyInfo return converter.getPrivateKey(keyInfo) } } Additionally, here is the code used to call the Apple authentication API from the backend server: @Service class AppleAuthService( private val appleProperties: AppleProperties, ) { private val logger = LoggerFactory.getLogger(javaClass) private val restTemplate = RestTemplate() fun getTokens(authorizationCode: String): TokenResponse { try { val clientSecret = makeClientSecret() val formData: MultiValueMap<String, String> = LinkedMultiValueMap() formData.add("client_id", appleProperties.clientId) formData.add("client_secret", clientSecret) formData.add("code", authorizationCode) formData.add("grant_type", "authorization_code") val headers = HttpHeaders() headers.contentType = MediaType.APPLICATION_FORM_URLENCODED val requestEntity = HttpEntity(formData, headers) val response = restTemplate.postForObject( "https://appleid.apple.com/auth/token", requestEntity, TokenResponse::class.java, ) return response ?: throw RuntimeException("Failed to retrieve tokens from Apple") } catch (ex: Exception) { logger.error("Error retrieving tokens: ", ex) throw ex } } data class TokenResponse( val access_token: String, val expires_in: Long, val id_token: String, val refresh_token: String, val token_type: String, ) Despite generating the client secret correctly, I am still receiving the invalid_client error when calling the API. Could you please help me identify the cause of this error and provide guidance on how to resolve it? Thank you.