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I'm trying to set up Sign In With Apple on my .NET 7 Web App (Not sure how many people here use this). I followed the guide by Scott Brady here: https://www.scottbrady91.com/openid-connect/implementing-sign-in-with-apple-in-aspnet-core It reaches Apple Sign In OK, authenticates, and passes back to my server, but the callback responds with this error. OpenIdConnectProtocolException: Message contains error: 'invalid_client', error_description: 'error_description is null', error_uri: 'error_uri is null'. Googling hasn't helped much, other than I saw a post saying to wait 48 hours, which I have now done (not that that makes sense anyway). Any idea whats been done wrong? Code below, replacing sensitive data. Startup.cs .AddOpenIdConnect("apple", async options => { options.Authority = "https://appleid.apple.com"; // disco doc: https://appleid.apple.com/.well-known/openid-configuration options.ClientId = "com.rackemapp.applelogin"; // Service ID options.CallbackPath = "/signin-apple"; // corresponding to your redirect URI options.ResponseType = "code id_token"; // hybrid flow due to lack of PKCE support options.ResponseMode = "form_post"; // form post due to prevent PII in the URL options.UsePkce = false; // apple does not currently support PKCE (April 2021) options.DisableTelemetry = true; options.Scope.Clear(); // apple does not support the profile scope options.Scope.Add("openid"); options.Scope.Add("email"); options.Scope.Add("name"); options.Events.OnAuthorizationCodeReceived = context => { context.TokenEndpointRequest.ClientSecret = AppleTokenGenerator.CreateNewToken(); return Task.CompletedTask; }; }); Apple Token Generator public static class AppleTokenGenerator { public static string CreateNewToken() { const string iss = "[MyTeamId]"; // your account's team ID found in the dev portal const string aud = "https://appleid.apple.com"; const string sub = "com.rackemapp.applelogin"; // same as client_id var now = DateTime.UtcNow; // contents of your .p8 file const string privateKey = "[MyKey]"; var ecdsa = ECDsa.Create(); ecdsa?.ImportPkcs8PrivateKey(Convert.FromBase64String(privateKey), out _); var handler = new JsonWebTokenHandler(); return handler.CreateToken(new SecurityTokenDescriptor { Issuer = iss, Audience = aud, Claims = new Dictionary<string, object> { { "sub", sub } }, Expires = now.AddMinutes(5), // expiry can be a maximum of 6 months - generate one per request or re-use until expiration IssuedAt = now, NotBefore = now, SigningCredentials = new SigningCredentials(new ECDsaSecurityKey(ecdsa), SecurityAlgorithms.EcdsaSha256) }); } } Also attached, images of my keys and setp in developer portal