Support

Yes, of course! SocialLogin is documented in its Wiki.

A word of caution. Login with Apple is convoluted. If you do not have an Apple Developer Account ($99 per year) you won't be able to do it at all. This method makes most sense if you have apps on Apple's App Store which use Login with Apple as well. Using the same application ID in the app and on your site you can create a unified login experience.

The message means that you have not entered the correct Services ID in the Client ID field of the plugin (see https://github.com/akeeba/sociallogin/wiki/Apple#create-a-services-id for the step where you created this).

For reference, here's what it looks on my blog (note that I've disabled it because nobody was using it and I'm not sure I will paying those hundred bucks a year for something nobody uses).

Make sure the Client ID is the same one you've used for the team whose ID you are using.

Check the Team ID and Key ID.

The KeyID starts with the Team ID. For example, if your Team ID is 1AB2C3D4E6 your Key ID will be something like 1AB2C3D4E6.com.example. The Key ID must be for a key made for Sign In with Apple.

The text contents of the key file you downloaded must be pasted into the Secret Key field.

Make sure that in https://developer.apple.com/account/resources/services/configure you have already verified SPF for both your domain and the email address you have set up in the email forwarding setup. Remember that you can only assign an email address to one set of domains. You cannot use the same email address on multiple domains.