Apple OAuth2 "Registration Not Complete" Error Despite Correct Configuration

I'm getting a "Registration Not Complete" error when implementing Apple Sign In OAuth2 on self-hosted Appwrite.

Environment: Self-hosted Appwrite (latest), iOS Swift/SwiftUI, custom HTTPS domain

Current Behavior: ✅ User clicks "Sign in with Apple" ✅ Redirects to Safari successfully ✅ Apple login page displays with user info (name, email) ❌ Shows "Sign Up Not Completed" error at bottom ❌ Cannot proceed with authorization

Configuration (all verified correct):

• Apple OAuth Provider enabled in Appwrite Console with Service ID, Key ID, Team ID, P8 file
• iOS Platform registered with correct Bundle ID
• Return URL matches exactly in both Appwrite and Apple Developer Console
• URL Scheme in Info.plist: appwrite-callback-{projectId}
• Apple Developer: Service ID configured, Primary App ID has "Sign in with Apple" enabled, Return URLs and Domains set correctly
• Nginx reverse proxy configured (callback returns 400, not 301)

Swift Implementation:

// Initialize
let client = Client().setEndpoint("https://...").setProject("...")
let account = Account(client)

// Start OAuth
try await account.createOAuth2Session(provider: .apple)

// Handle callback
.onOpenURL { url in
    guard url.scheme == "appwrite-callback-{projectId}" else { return }
    let user = try await account.get()
}

What I've Tried:

• Verified Return URL exact match (no trailing slash)
• Waited 2+ hours for Apple config propagation
• Reinstalled app multiple times
• Followed both official Appwrite tutorials
• All configurations match documentation

Questions:

1. Is there additional config needed for self-hosted vs Cloud for Apple OAuth?
2. Does iOS Platform need a "Hostname" field in self-hosted versions?
3. Any known issues with Apple OAuth on self-hosted Appwrite?

The OAuth flow starts successfully but fails at Apple's validation. Any help appreciated!