diff --git a/src/backend/accounts/progress.ts b/src/backend/accounts/progress.ts
index 6b522079..511d1c5d 100644
--- a/src/backend/accounts/progress.ts
+++ b/src/backend/accounts/progress.ts
@@ -2,7 +2,6 @@ import { ofetch } from "ofetch";
 
 import { getAuthHeaders } from "@/backend/accounts/auth";
 import { ProgressResponse } from "@/backend/accounts/user";
-import { BACKEND_URL } from "@/setup/constants";
 import { AccountWithToken } from "@/stores/auth";
 import { ProgressMediaItem, ProgressUpdateItem } from "@/stores/progress";
 
@@ -104,7 +103,6 @@ export async function removeProgress(
   episodeId?: string,
   seasonId?: string,
 ) {
-  if (!BACKEND_URL) return;
   await ofetch(`/users/${account.userId}/progress/${id}`, {
     method: "DELETE",
     headers: getAuthHeaders(account.token),
diff --git a/src/hooks/auth/useAuth.ts b/src/hooks/auth/useAuth.ts
index f608d148..3ce49163 100644
--- a/src/hooks/auth/useAuth.ts
+++ b/src/hooks/auth/useAuth.ts
@@ -63,6 +63,7 @@ export function useAuth() {
 
   const login = useCallback(
     async (loginData: LoginData) => {
+      if (!backendUrl) return;
       const keys = await keysFromMnemonic(loginData.mnemonic);
       const publicKeyBase64Url = bytesToBase64Url(keys.publicKey);
       const { challenge } = await getLoginChallengeToken(
@@ -87,7 +88,7 @@ export function useAuth() {
   );
 
   const logout = useCallback(async () => {
-    if (!currentAccount) return;
+    if (!currentAccount || !backendUrl) return;
     try {
       await removeSession(
         backendUrl,
@@ -102,6 +103,7 @@ export function useAuth() {
 
   const register = useCallback(
     async (registerData: RegistrationData) => {
+      if (!backendUrl) return;
       const { challenge } = await getRegisterChallengeToken(
         backendUrl,
         registerData.recaptchaToken,
@@ -134,6 +136,7 @@ export function useAuth() {
       progressItems: Record<string, ProgressMediaItem>,
       bookmarks: Record<string, BookmarkMediaItem>,
     ) => {
+      if (!backendUrl) return;
       if (
         Object.keys(progressItems).length === 0 &&
         Object.keys(bookmarks).length === 0
@@ -159,6 +162,7 @@ export function useAuth() {
 
   const restore = useCallback(
     async (account: AccountWithToken) => {
+      if (!backendUrl) return;
       let user: { user: UserResponse; session: SessionResponse };
       try {
         user = await getUser(backendUrl, account.token);
diff --git a/src/hooks/auth/useBackendUrl.ts b/src/hooks/auth/useBackendUrl.ts
index e417ed06..64545227 100644
--- a/src/hooks/auth/useBackendUrl.ts
+++ b/src/hooks/auth/useBackendUrl.ts
@@ -1,7 +1,7 @@
 import { conf } from "@/setup/config";
 import { useAuthStore } from "@/stores/auth";
 
-export function useBackendUrl() {
+export function useBackendUrl(): string | undefined {
   const backendUrl = useAuthStore((s) => s.backendUrl);
   return backendUrl ?? conf().BACKEND_URL;
 }
diff --git a/src/pages/Settings.tsx b/src/pages/Settings.tsx
index 18b755ca..cebf1ddd 100644
--- a/src/pages/Settings.tsx
+++ b/src/pages/Settings.tsx
@@ -70,6 +70,7 @@ export function AccountSettings(props: {
   const url = useBackendUrl();
   const { account } = props;
   const [sessionsResult, execSessions] = useAsyncFn(() => {
+    if (!url) return Promise.resolve([]);
     return getSessions(url, account);
   }, [account, url]);
   useEffect(() => {
@@ -144,7 +145,7 @@ export function SettingsPage() {
   );
 
   const saveChanges = useCallback(async () => {
-    if (account) {
+    if (account && backendUrl) {
       if (
         state.appLanguage.changed ||
         state.theme.changed ||
diff --git a/src/pages/onboarding/OnboardingProxy.tsx b/src/pages/onboarding/OnboardingProxy.tsx
index e67c0769..00584eef 100644
--- a/src/pages/onboarding/OnboardingProxy.tsx
+++ b/src/pages/onboarding/OnboardingProxy.tsx
@@ -43,7 +43,7 @@ export function OnboardingProxyPage() {
         throw new Error("onboarding.proxy.input.errorNotProxy");
       setProxySet([url]);
 
-      if (account) {
+      if (account && backendUrl) {
         await updateSettings(backendUrl, account, {
           proxyUrls: [url],
         });
diff --git a/src/pages/parts/admin/BackendTestPart.tsx b/src/pages/parts/admin/BackendTestPart.tsx
index 449e9643..aadd9397 100644
--- a/src/pages/parts/admin/BackendTestPart.tsx
+++ b/src/pages/parts/admin/BackendTestPart.tsx
@@ -32,13 +32,21 @@ export function BackendTestPart() {
       value: null,
     });
 
+    if (!backendUrl) {
+      return setStatus({
+        hasTested: true,
+        success: false,
+        errorText: "Backend URL is not set",
+        value: null,
+      });
+    }
+
     try {
       const backendData = await getBackendMeta(backendUrl);
       return setStatus({
         hasTested: true,
         success: true,
-        errorText:
-          "Failed to call backend, double check the URL key and your internet connection",
+        errorText: "",
         value: backendData,
       });
     } catch (err) {
@@ -46,7 +54,7 @@ export function BackendTestPart() {
         hasTested: true,
         success: false,
         errorText:
-          "Failed to call backend, double check the URL key and your internet connection",
+          "Failed to call backend, double check the URL, your internet connection, and ensure CORS is properly configured on your backend.",
         value: null,
       });
     }
diff --git a/src/pages/parts/auth/LoginFormPart.tsx b/src/pages/parts/auth/LoginFormPart.tsx
index e4bed3ec..ac63fad2 100644
--- a/src/pages/parts/auth/LoginFormPart.tsx
+++ b/src/pages/parts/auth/LoginFormPart.tsx
@@ -52,6 +52,9 @@ export function LoginFormPart(props: LoginFormPartProps) {
         throw err;
       }
 
+      if (!account)
+        throw new Error(t("auth.login.validationError") ?? undefined);
+
       await importData(account, progressItems, bookmarkItems);
 
       await restore(account);
diff --git a/src/pages/parts/auth/TrustBackendPart.tsx b/src/pages/parts/auth/TrustBackendPart.tsx
index 3fa818ef..0d71e403 100644
--- a/src/pages/parts/auth/TrustBackendPart.tsx
+++ b/src/pages/parts/auth/TrustBackendPart.tsx
@@ -22,8 +22,12 @@ interface TrustBackendPartProps {
 export function TrustBackendPart(props: TrustBackendPartProps) {
   const navigate = useNavigate();
   const backendUrl = useBackendUrl();
-  const hostname = useMemo(() => new URL(backendUrl).hostname, [backendUrl]);
+  const hostname = useMemo(
+    () => (backendUrl ? new URL(backendUrl).hostname : ""),
+    [backendUrl],
+  );
   const result = useAsync(() => {
+    if (!backendUrl) return Promise.resolve(null);
     return getBackendMeta(backendUrl);
   }, [backendUrl]);
   const { t } = useTranslation();
diff --git a/src/pages/parts/auth/VerifyPassphrasePart.tsx b/src/pages/parts/auth/VerifyPassphrasePart.tsx
index 2f040ccb..1d6ea62a 100644
--- a/src/pages/parts/auth/VerifyPassphrasePart.tsx
+++ b/src/pages/parts/auth/VerifyPassphrasePart.tsx
@@ -47,6 +47,8 @@ export function VerifyPassphrase(props: VerifyPassphraseProps) {
 
   const [result, execute] = useAsyncFn(
     async (inputMnemonic: string) => {
+      if (!backendUrl)
+        throw new Error(t("auth.verify.noBackendUrl") ?? undefined);
       if (!props.mnemonic || !props.userData)
         throw new Error(t("auth.verify.invalidData") ?? undefined);
 
@@ -68,6 +70,9 @@ export function VerifyPassphrase(props: VerifyPassphraseProps) {
         recaptchaToken,
       });
 
+      if (!account)
+        throw new Error(t("auth.verify.registrationFailed") ?? undefined);
+
       await importData(account, progressItems, bookmarkItems);
 
       await updateSettings(backendUrl, account, {
diff --git a/src/pages/parts/settings/AccountActionsPart.tsx b/src/pages/parts/settings/AccountActionsPart.tsx
index e19aa9e9..f1e50dbf 100644
--- a/src/pages/parts/settings/AccountActionsPart.tsx
+++ b/src/pages/parts/settings/AccountActionsPart.tsx
@@ -18,7 +18,7 @@ export function AccountActionsPart() {
   const deleteModal = useModal("account-delete");
 
   const [deleteResult, deleteExec] = useAsyncFn(async () => {
-    if (!account) return;
+    if (!account || !url) return;
     await deleteUser(url, account);
     await logout();
     deleteModal.hide();
diff --git a/src/pages/parts/settings/DeviceListPart.tsx b/src/pages/parts/settings/DeviceListPart.tsx
index afaea589..c7326059 100644
--- a/src/pages/parts/settings/DeviceListPart.tsx
+++ b/src/pages/parts/settings/DeviceListPart.tsx
@@ -24,6 +24,7 @@ export function Device(props: {
   const token = useAuthStore((s) => s.account?.token);
   const [result, exec] = useAsyncFn(async () => {
     if (!token) throw new Error("No token present");
+    if (!url) throw new Error("No backend set");
     await removeSession(url, token, props.id);
     props.onRemove?.();
   }, [url, token, props.id]);
diff --git a/src/pages/parts/settings/SidebarPart.tsx b/src/pages/parts/settings/SidebarPart.tsx
index 47469a5e..13db06fe 100644
--- a/src/pages/parts/settings/SidebarPart.tsx
+++ b/src/pages/parts/settings/SidebarPart.tsx
@@ -14,9 +14,9 @@ import { useAuthStore } from "@/stores/auth";
 
 const rem = 16;
 
-function SecureBadge(props: { url: string }) {
+function SecureBadge(props: { url: string | undefined }) {
   const { t } = useTranslation();
-  const secure = props.url.startsWith("https://");
+  const secure = props.url ? props.url.startsWith("https://") : false;
   return (
     <div className="flex items-center gap-1 -mx-1 ml-3 px-1 rounded bg-largeCard-background font-bold">
       <Icon icon={secure ? Icons.LOCK : Icons.UNLOCK} />
@@ -68,6 +68,7 @@ export function SidebarPart() {
   const backendUrl = useBackendUrl();
 
   const backendMeta = useAsync(async () => {
+    if (!backendUrl) return;
     return getBackendMeta(backendUrl);
   }, [backendUrl]);
 
@@ -159,7 +160,7 @@ export function SidebarPart() {
                 <SecureBadge url={backendUrl} />
               </div>
               <p className="text-white">
-                {backendUrl.replace(/https?:\/\//, "")}
+                {backendUrl?.replace(/https?:\/\//, "") ?? "—"}
               </p>
             </div>
 
diff --git a/src/stores/bookmarks/BookmarkSyncer.tsx b/src/stores/bookmarks/BookmarkSyncer.tsx
index 1f3b705d..7d4d0bc0 100644
--- a/src/stores/bookmarks/BookmarkSyncer.tsx
+++ b/src/stores/bookmarks/BookmarkSyncer.tsx
@@ -60,6 +60,7 @@ export function BookmarkSyncer() {
   useEffect(() => {
     const interval = setInterval(() => {
       (async () => {
+        if (!url) return;
         const state = useBookmarkStore.getState();
         const user = useAuthStore.getState();
         await syncBookmarks(
diff --git a/src/stores/progress/ProgressSyncer.tsx b/src/stores/progress/ProgressSyncer.tsx
index c9b4eb58..67aae877 100644
--- a/src/stores/progress/ProgressSyncer.tsx
+++ b/src/stores/progress/ProgressSyncer.tsx
@@ -62,6 +62,7 @@ export function ProgressSyncer() {
   useEffect(() => {
     const interval = setInterval(() => {
       (async () => {
+        if (!url) return;
         const state = useProgressStore.getState();
         const user = useAuthStore.getState();
         await syncProgress(
diff --git a/src/stores/subtitles/SettingsSyncer.tsx b/src/stores/subtitles/SettingsSyncer.tsx
index 48b25bbe..ca3c0817 100644
--- a/src/stores/subtitles/SettingsSyncer.tsx
+++ b/src/stores/subtitles/SettingsSyncer.tsx
@@ -16,6 +16,7 @@ export function SettingsSyncer() {
   useEffect(() => {
     const interval = setInterval(() => {
       (async () => {
+        if (!url) return;
         const state = useSubtitleStore.getState();
         const user = useAuthStore.getState();
         if (state.lastSync.lastSelectedLanguage === state.lastSelectedLanguage)