diff --git a/server/api/[server]/oauth/[origin].ts b/server/api/[server]/oauth/[origin].ts
index 66833146..c5555354 100644
--- a/server/api/[server]/oauth/[origin].ts
+++ b/server/api/[server]/oauth/[origin].ts
@@ -1,6 +1,6 @@
 import { stringifyQuery } from 'ufo'
 
-import { defaultUserAgent } from '~~/server/utils/shared'
+import { defaultUserAgent, invalidateApp } from '~~/server/utils/shared'
 
 export default defineEventHandler(async (event) => {
   let { server, origin } = getRouterParams(event)
@@ -43,7 +43,51 @@ export default defineEventHandler(async (event) => {
     const url = `/signin/callback?${stringifyQuery({ server, token: result.access_token, vapid_key: app.vapid_key })}`
     await sendRedirect(event, url, 302)
   }
-  catch {
+  catch (error: any) {
+    // Check for invalid client error (OAuth app deleted)
+    if (error?.data?.error === 'invalid_client'
+      || (error?.statusCode === 401 && error?.data?.error_description?.includes('Client authentication failed'))) {
+      // Invalidate cached app and retry once
+      await invalidateApp(origin, server)
+
+      try {
+        const newApp = await getApp(origin, server)
+        if (!newApp) {
+          throw createError({
+            statusCode: 400,
+            statusMessage: `Failed to re-register app for server: ${server}`,
+          })
+        }
+
+        const retryResult: any = await $fetch(`https://${server}/oauth/token`, {
+          method: 'POST',
+          headers: {
+            'user-agent': defaultUserAgent,
+          },
+          body: {
+            client_id: newApp.client_id,
+            client_secret: newApp.client_secret,
+            redirect_uri: getRedirectURI(origin, server),
+            grant_type: 'authorization_code',
+            code,
+            scope: 'read write follow push',
+          },
+          retry: 1,
+        })
+
+        const url = `/signin/callback?${stringifyQuery({ server, token: retryResult.access_token, vapid_key: newApp.vapid_key })}`
+        await sendRedirect(event, url, 302)
+        return
+      }
+      catch {
+        throw createError({
+          statusCode: 400,
+          statusMessage: 'OAuth application recovery failed. Please try again.',
+        })
+      }
+    }
+
+    // Other errors (network, invalid code, etc.)
     throw createError({
       statusCode: 400,
       statusMessage: 'Could not complete log in.',
diff --git a/server/utils/shared.ts b/server/utils/shared.ts
index 35ef064b..54faa53c 100644
--- a/server/utils/shared.ts
+++ b/server/utils/shared.ts
@@ -111,6 +111,12 @@ export async function deleteApp(server: string) {
     await storage.removeItem(key)
 }
 
+export async function invalidateApp(origin: string, server: string) {
+  const host = origin.replace(/^https?:\/\//, '').replace(/\W/g, '-').replace(/\?.*$/, '')
+  const key = `servers:v4:${server}:${host}.json`.toLowerCase()
+  await storage.removeItem(key)
+}
+
 export async function listServers() {
   const keys = await storage.getKeys('servers:v4:')
   const servers = new Set<string>()