fix(frontend): improve waitlist error display for users not on allowlist

- Updated EmailNotAllowedModal with clear waitlist CTA and helpful messaging
- Added "Join Waitlist" button that opens https://agpt.co/waitlist
- Fixed OAuth provider signup/login to properly display waitlist modal
- Enhanced auth-code-error page to detect and display waitlist errors
- Added helpful guidance about checking email and Discord support link
- Consistent waitlist error handling across all auth flows

Fixes OPEN-2794

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

autogpt_platform/frontend/src/app/(platform)/auth/auth-code-error/page.tsx

@@ -2,11 +2,16 @@
 
 import { isServerSide } from "@/lib/utils/is-server-side";
 import { useEffect, useState } from "react";
+import { Button } from "@/components/atoms/Button/Button";
+import { Text } from "@/components/atoms/Text/Text";
+import { Card } from "@/components/atoms/Card/Card";
+import { useRouter } from "next/navigation";
 
 export default function AuthErrorPage() {
   const [errorType, setErrorType] = useState<string | null>(null);
   const [errorCode, setErrorCode] = useState<string | null>(null);
   const [errorDescription, setErrorDescription] = useState<string | null>(null);
+  const router = useRouter();
 
   useEffect(() => {
     // This code only runs on the client side
@@ -23,15 +28,105 @@ export default function AuthErrorPage() {
   }, []);
 
   if (!errorType && !errorCode && !errorDescription) {
-    return <div>Loading...</div>;
+    return (
+      <div className="flex h-screen items-center justify-center">
+        <Text variant="body">Loading...</Text>
+      </div>
+    );
   }
 
+  // Check if this is a waitlist/not allowed error
+  const isWaitlistError =
+    errorCode === "403" ||
+    errorDescription?.toLowerCase().includes("not allowed") ||
+    errorDescription?.toLowerCase().includes("waitlist") ||
+    errorDescription?.toLowerCase().includes("allowlist");
+
+  if (isWaitlistError) {
+    return (
+      <div className="flex h-screen items-center justify-center">
+        <Card className="w-full max-w-md p-8">
+          <div className="flex flex-col items-center gap-6">
+            <Text variant="h3">Join the Waitlist</Text>
+            <div className="flex flex-col gap-4 text-center">
+              <Text variant="body">
+                AutoGPT Platform is currently in closed beta. Your email address
+                isn&apos;t on our current allowlist for early access.
+              </Text>
+              <Text variant="small" className="text-muted-foreground">
+                Join our waitlist to get notified when we open up access!
+              </Text>
+            </div>
+            <div className="flex gap-3">
+              <Button
+                variant="secondary"
+                onClick={() => {
+                  window.open("https://agpt.co/waitlist", "_blank");
+                }}
+              >
+                Join Waitlist
+              </Button>
+              <Button variant="primary" onClick={() => router.push("/login")}>
+                Back to Login
+              </Button>
+            </div>
+            <div className="flex flex-col gap-2">
+              <Text
+                variant="small"
+                className="text-center text-muted-foreground"
+              >
+                Already signed up for the waitlist? Make sure you&apos;re using
+                the exact same email address you used when signing up.
+              </Text>
+              <Text
+                variant="small"
+                className="text-center text-muted-foreground"
+              >
+                If you&apos;re not sure which email you used or need help,{" "}
+                <a
+                  href="https://discord.gg/autogpt"
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  className="underline hover:text-foreground"
+                >
+                  reach out on Discord
+                </a>
+              </Text>
+            </div>
+          </div>
+        </Card>
+      </div>
+    );
+  }
+
+  // Default error display for other types of errors
   return (
-    <div>
-      <h1>Authentication Error</h1>
-      {errorType && <p>Error Type: {errorType}</p>}
-      {errorCode && <p>Error Code: {errorCode}</p>}
-      {errorDescription && <p>Error Description: {errorDescription}</p>}
+    <div className="flex h-screen items-center justify-center">
+      <Card className="w-full max-w-md p-8">
+        <div className="flex flex-col items-center gap-6">
+          <Text variant="h3">Authentication Error</Text>
+          <div className="flex flex-col gap-2 text-center">
+            {errorType && (
+              <Text variant="body">
+                <strong>Error Type:</strong> {errorType}
+              </Text>
+            )}
+            {errorCode && (
+              <Text variant="body">
+                <strong>Error Code:</strong> {errorCode}
+              </Text>
+            )}
+            {errorDescription && (
+              <Text variant="body">
+                <strong>Description:</strong> {errorDescription}
+              </Text>
+            )}
+          </div>
+          <Button variant="primary" onClick={() => router.push("/login")}>
+            Back to Login
+          </Button>
+        </div>
+      </Card>
     </div>
   );
 }

autogpt_platform/frontend/src/app/(platform)/login/useLoginPage.ts

@@ -67,7 +67,7 @@ export function useLoginPage() {
 
       if (!response.ok) {
         const { error } = await response.json();
-        if (typeof error === "string" && error.includes("not_allowed")) {
+        if (error === "not_allowed") {
           setShowNotAllowedModal(true);
         } else {
           setFeedback(error || "Failed to start OAuth flow");

autogpt_platform/frontend/src/app/(platform)/signup/useSignupPage.ts

@@ -70,6 +70,13 @@ export function useSignupPage() {
         const { error } = await response.json();
         setIsGoogleLoading(false);
         resetCaptcha();
+
+        // Check for waitlist error
+        if (error === "not_allowed") {
+          setShowNotAllowedModal(true);
+          return;
+        }
+
         toast({
           title: error || "Failed to start OAuth flow",
           variant: "destructive",

autogpt_platform/frontend/src/components/auth/EmailNotAllowedModal.tsx

@@ -15,16 +15,45 @@ export function EmailNotAllowedModal({ isOpen, onClose }: Props) {
     >
       <Dialog.Content>
         <div className="flex flex-col items-center gap-8 py-4">
-          <Text variant="h3">Access Restricted</Text>
-          <Text variant="large-medium" className="text-center">
-            We&apos;re currently in a limited access phase. Your email address
-            isn&apos;t on our current allowlist for early access. If you believe
-            this is an error or would like to request access, please contact us.
-          </Text>
-          <div className="flex justify-end pt-4">
-            <Button variant="primary" onClick={onClose}>
-              I understand
+          <Text variant="h3">Join the Waitlist</Text>
+          <div className="flex flex-col gap-4">
+            <Text variant="large-medium" className="text-center">
+              AutoGPT Platform is currently in closed beta. Your email address
+              isn&apos;t on our current allowlist for early access.
+            </Text>
+            <Text variant="body" className="text-center">
+              Join our waitlist to get notified when we open up access!
+            </Text>
+          </div>
+          <div className="flex gap-3">
+            <Button
+              variant="secondary"
+              onClick={() => {
+                window.open("https://agpt.co/waitlist", "_blank");
+              }}
+            >
+              Join Waitlist
             </Button>
+            <Button variant="primary" onClick={onClose}>
+              Close
+            </Button>
+          </div>
+          <div className="flex flex-col gap-2">
+            <Text variant="small" className="text-center text-muted-foreground">
+              Already signed up for the waitlist? Make sure you&apos;re using
+              the exact same email address you used when signing up.
+            </Text>
+            <Text variant="small" className="text-center text-muted-foreground">
+              If you&apos;re not sure which email you used or need help,{" "}
+              <a
+                href="https://discord.gg/autogpt"
+                target="_blank"
+                rel="noopener noreferrer"
+                className="underline hover:text-foreground"
+              >
+                reach out on Discord
+              </a>
+            </Text>
           </div>
         </div>
       </Dialog.Content>