Be careful because of this invalid_client error could be misleading (as always Apple's error messages) $postParams = array( 'code' => ..., 'client_id' => ..., 'client_secret' => ..., 'grant_type' => 'authorization_code', 'redirect_uri' => ..., ); $curl = curl_init('https://appleid.apple.com/auth/token'); // never pass params as just array for apple without stringifying via http_build_query() curl_setopt($curl, CURLOPT_POSTFIELDS, http_build_query($postParams)); When you will use just curl_setopt($curl, CURLOPT_POSTFIELDS, $postParams); it is valid POST request but another type than Apple expects but lazy apple developers are not able to provide error that this type of POST request is unsupported.

After tens of messages with apple support and many irrelevant answers and many excuses I finally got this answer... > Our engineering teams have found that the validation job is seeing closed connections while trying to fetch the SSL certs. > > To provide more context, when the validation job tries reaching the client host at the verification file URL path and encounters an HTTP 200 response, it will re-use the open connection and acquire the SSL cert information (to check for expiration as well as to ensure no changes to the Subject and Issuer in the SSL cert chain have been made from the previous domain registration). This is where the issue for automated validation is occurring for your domains. > > They recommend for you to further review the timeout settings and adjust if needed. > > We appreciate the feedback you have provided to the verification process. Our teams are exploring ways to enhance and improve the domain validation process. Interesting is that any browser including Safari can access SSL cert info, also https://www.ssllabs.com/ssltest have no problem to validate cert, just nobody has problem except Apple. Also interesting is when I click "Verify manually" Apple succeed verification? Just then there is no connection close problem? But when Apple should do it automatically suddenly there is a some problem with closing connections? Im really loosing any hope that Apple will sometime fix this annoying bug.

@mmasato this bug is active also nowadays. Did you find solution please? Im wondered that on the internet there arw no mentions about it.

Exactly. In my bug report via black hole Apple Feedback Assistant I exchanged in about 20 messages with Apple support. They wrote just excuses etc. Later wrote that they have some problem with Lets Encrypt cert. Strange because of certs are world-wide accepted, most popular certs, every browser accept it including Safari but Apple engineers have problem with validating our websites with Lets Encrypt certs. Thanks for all. We annoyed them for so long that they admitted that the problem is on their side and they are preparing an improvement. Question is how many years it will take.

This is typical Apple. Iphone 6 with iOS 12 is nowadays still supported by Apple (only iPhone 5* does not have support) but you do not have any way how to test it! Simulators support only newer devices! Thank you great Apple!

Terrible problem. We can add as many APP ids as we want but grouping supports just 5. We successfully configured Facebook and also Google sign-in for in about 10 app variants but it is not possible for Apple. Apple should increase this useless low limit.

No. Information in Membership details are some another. If I want to edit bank account holder apple offers checkbox "Use the same as Legal Entity" and when I check it, it fill-in address with typos errors. In membership details address is correct. So question is that where else have Apple stored "Legal Entity" information to edit it?