This resolves the issue of being unable to obtain the client's IP address due to the IPv6 format.

src/lib/ip.ts

@@ -1,3 +1,5 @@
+import ipaddr from 'ipaddr.js';
+
 export const IP_ADDRESS_HEADERS = [
   'true-client-ip', // CDN
   'cf-connecting-ip', // Cloudflare
@@ -13,35 +15,87 @@ export const IP_ADDRESS_HEADERS = [
   'x-forwarded',
 ];
 
+/**
+ * Normalize IP strings to a canonical form:
+ * - strips IPv4-mapped IPv6 (e.g. ::ffff:192.0.2.1 -> 192.0.2.1)
+ * - keeps valid IPv4/IPv6 as-is (canonically formatted by ipaddr.js)
+ */
+function normalizeIp(ip?: string | null) {
+  if (!ip) return ip;
+
+  try {
+    const parsed = ipaddr.parse(ip);
+
+    if (parsed.kind() === 'ipv6' && (parsed as ipaddr.IPv6).isIPv4MappedAddress()) {
+      return (parsed as ipaddr.IPv6).toIPv4Address().toString();
+    }
+
+    return parsed.toString();
+  } catch {
+    // Fallback: return original if parsing fails
+    return ip;
+  }
+}
+
+function resolveIp(ip?: string | null) {
+  if (!ip) return ip;
+
+  // First, try as-is
+  const normalized = normalizeIp(ip);
+  try {
+    ipaddr.parse(normalized);
+    return normalized;
+  } catch {
+    // try stripping port (handles IPv4:port; leaves IPv6 intact)
+    const stripped = stripPort(ip);
+    if (stripped !== ip) {
+      const normalizedStripped = normalizeIp(stripped);
+      try {
+        ipaddr.parse(normalizedStripped);
+        return normalizedStripped;
+      } catch {
+        return normalizedStripped;
+      }
+    }
+
+    return normalized;
+  }
+}
+
 export function getIpAddress(headers: Headers) {
   const customHeader = process.env.CLIENT_IP_HEADER;
 
   if (customHeader && headers.get(customHeader)) {
-    return headers.get(customHeader);
+    return resolveIp(headers.get(customHeader));
   }
 
-  const header = IP_ADDRESS_HEADERS.find(name => {
+  const header = IP_ADDRESS_HEADERS.find(name => headers.get(name));
-    return headers.get(name);
+  if (!header) {
-  });
+    return undefined;
+  }
 
   const ip = headers.get(header);
 
   if (header === 'x-forwarded-for') {
-    return ip?.split(',')?.[0]?.trim();
+    return resolveIp(ip?.split(',')?.[0]?.trim());
   }
 
   if (header === 'forwarded') {
     const match = ip.match(/for=(\[?[0-9a-fA-F:.]+\]?)/);
 
     if (match) {
-      return match[1];
+      return resolveIp(match[1]);
     }
   }
 
-  return ip;
+  return resolveIp(ip);
 }
 
-export function stripPort(ip: string) {
+export function stripPort(ip?: string | null) {
+  if (!ip) {
+    return ip;
+  }
+
   if (ip.startsWith('[')) {
     const endBracket = ip.indexOf(']');
     if (endBracket !== -1) {