Common Replit Issues

Third-party API returns 429 Too Many Requests. You're hitting rate limits and requests are being rejected.

Replit apps can generate many rapid requests, quickly hitting API quotas.

Your app hangs when calling external APIs. Requests to third-party services timeout without response.

Network latency and Replit's resource constraints cause slow API calls.

Your API endpoint returns 404 Not Found even though you defined it. The route isn't being registered or accessed incorrectly.

Routing misconfiguration or incorrect request path causes 404s.

API calls fail with CORS error: 'Access to XMLHttpRequest blocked by CORS policy'. Browsers block requests from your frontend to your API.

Same-origin policy requires explicit CORS configuration.

Same charge processes multiple times if request retries. Customers are charged twice for one payment.

Idempotency keys prevent duplicate processing on network retries.

Your app uses Stripe test API keys in production. Charges aren't processing, or test data appears in live account.

Key mismatch between test and production environment breaks payment processing.

File upload fails with 400 Bad Request or files aren't received. Multipart form handling has issues.

Multipart form configuration and size limits require proper setup.

Authenticated API requests fail because cookies aren't sent. CORS blocks credentials even after preflight succeeds.

Credentials mode and CORS headers must align for cookies to transmit.

API returns 400 Bad Request with validation errors. Request payload doesn't match expected format or constraints.

Request validation catches invalid or malformed data before processing.

Stripe webhook events aren't received by your Replit app. Payment events aren't being processed, leaving orders in pending state.

Webhook delivery can fail for many reasons including endpoint accessibility and signature mismatches.

Stripe webhook calls are rejected with signature verification error. Webhook handler rejects all incoming events.

Signature verification requires exact configuration and secret key matching.

Spring Actuator endpoints (/actuator/metrics, /actuator/health) return 401 Unauthorized. Metrics and health checks are blocked.

Security configuration restricts actuator access inappropriately.

API returns unexpected response format causing JSON parsing errors. The response doesn't match expected structure.

Missing fields, unexpected types, or null values break deserialization.

OAuth providers reject your Replit application with invalid redirect URI or misconfigured credentials. Your login flow fails when redirecting back from the OAuth provider.

This commonly happens when the redirect URI registered with the OAuth provider doesn't match your Replit deployment domain or when environment variables are missing.

Users are logged out when your Replit app restarts or scales. Session data stored in memory is lost, forcing users to re-authenticate. This is critical for production apps.

Replit deployments can restart unexpectedly, and memory-based sessions don't persist across those events.

Your app fails to authenticate with GitHub API using stored tokens. The token is rejected as invalid, expired, or lacking required scopes.

GitHub tokens have expiration dates and scope limitations that must match your API usage.

You can't access or modify Replit Secrets because two-factor authentication is required but not set up. This blocks you from updating API keys and credentials.

Replit enforces 2FA for sensitive operations in high-security projects.

Your app crashes or behaves incorrectly because environment variables aren't set. Required configuration is missing.

Environment variables must be set in Replit Secrets for app to access them.

CSRF attacks succeed despite enabled CSRF protection. Malicious sites can perform unauthorized actions.

CSRF tokens not properly validated or exempt endpoints allow attacks.

Remember-me tokens are exposed in logs or storage. Session tokens compromise account security if leaked.

Persistent authentication tokens require secure storage and rotation.

Your app responds slowly and database queries take seconds. Database operations are the bottleneck preventing good user experience.

Replit's shared resources and unoptimized queries compound to create significant latency.

SQLite database is locked and transactions timeout. Multiple processes are trying to write simultaneously, causing lock contention.

SQLite isn't designed for concurrent writes like PostgreSQL, making it unsuitable for Replit's multi-process environment.

Your application fails to connect to PostgreSQL with a connection refused error. The database service is either not running or your connection string is incorrect.

Replit's PostgreSQL requires the correct credentials, port, and hostname which vary between development and production.

Your application crashes with 'sorry, too many clients already' error. The PostgreSQL connection pool has hit its maximum limit.

Replit's PostgreSQL has a limited connection pool, and connections may not be properly released.

Your application fails to start because Flyway migration encounters an error. The database schema update is blocked, preventing the app from initializing.

Migration failures often indicate SQL syntax errors, constraint violations, or state mismatches between environments.

App is vulnerable to SQL injection attacks. Malicious input can modify or extract database data. Security audit fails.

String concatenation in SQL queries allows attackers to inject SQL code.

Connection pool errors or timeout exceptions appear in logs. HikariCP is misconfigured for Replit's resource constraints.

Connection pool size, timeout, and idle settings must match Replit's limited database connections.

Deployment hangs and times out before completion. Build or startup phase exceeds Replit's time limit.

Large dependencies, slow network, or inefficient startup sequences cause timeouts.

Your app builds successfully but crashes immediately after deployment starts. The app container exits with an error before becoming healthy.

This typically indicates environment configuration issues, missing dependencies, or startup errors.

Kotlin compilation fails with type or null safety errors. Build aborts before completion.

Kotlin's strict null safety and type system catch errors at compile time.

App fails to start with circular dependency error. Two or more beans reference each other creating an unsolvable dependency chain.

Spring can't instantiate beans if they depend on each other.

Build fails with Gradle version incompatibility errors. gradle wrapper expects different version than installed.

Gradle version conflicts prevent proper builds.

Your app fails to start with 'Address already in use' or 'bind: permission denied' error. The port is already bound by another process.

Replit may have lingering processes from previous deployments still listening on the port.

Replit displays config errors or your custom run command doesn't execute. The .replit configuration file has syntax errors or missing required fields.

The .replit file controls how your app builds and runs on Replit.

Your app runs out of memory (OOM) and crashes on Replit Reserved VM. Even with memory limits increased, the app consumes all available RAM.

Spring Boot and the JVM have significant base memory overhead.

Your AI agent continuously loops without reaching a goal, consuming resources and never terminating. Agent runs infinitely instead of completing.

Insufficient loop detection and termination conditions cause runaway agents.

Asynchronous requests timeout before completing, even though operation should finish quickly. Async operations hang indefinitely.

Misconfigured timeout values or blocking operations in async code cause hangs.

Your AI agent makes poor decisions, gives wrong answers, or misunderstands user intent. Accuracy is too low for production use.

Unclear prompts, poor context, or inadequate tools reduce agent effectiveness.

Your AI agent consumes excessive tokens causing high API costs. Each request uses thousands of tokens unnecessarily.

Verbose prompts, large context windows, and inefficient tool use waste tokens.

Your app takes 30+ seconds to start, making development slow and deployments take forever. Startup time is unacceptable.

Spring Boot's autoconfiguration and component scanning cause slow initialization.

App consumes excessive memory causing slowdowns or OOM errors. Memory usage grows continuously or spikes during certain operations.

Memory leaks or inefficient data structures cause runaway memory consumption.

First request to your deployed app takes 10+ seconds. Cold start is very slow before the app becomes responsive.

JVM warmup, container startup, and initialization all compound.

App fails with 'command not found' or 'library not found' error. A required system dependency isn't in Replit's Nix environment.

Replit uses Nix for reproducible environments, requiring explicit dependency declarations.

Gradle builds take 2-3 minutes even for small changes. Build process is frustratingly slow.

Replit's shared resources and Gradle's large classpath cause slow compilation.

WebSocket connections fail with network errors or close immediately. Real-time features like chat or notifications don't work.

WebSocket configuration and deployment differences between local and Replit cause issues.

Thymeleaf templates fail to render with parsing or expression errors. App shows error page instead of rendered content.

Template syntax errors, missing context variables, or incorrect expressions break rendering.

CSS, JavaScript, and images return 404 or don't load on deployed Replit app. Static resources are missing or misconfigured.

Spring Boot has specific requirements for static file locations and configuration.

CSS or JavaScript changes don't appear after deployment. Browser caches old versions. Users see old styles or functionality.

Aggressive caching hides code updates.

App displays incorrectly on mobile devices with layout breaking, text too small, or elements overlapping. Responsive design isn't working.

Missing viewport meta tag or CSS media queries cause mobile rendering issues.

XSS attacks are possible through template injection. Attacker-controlled input executes JavaScript on victim's browser.

Improper escaping of user input in templates allows script execution.

Browser shows mixed content warning or blocks insecure resources. Deployed app mixes secure HTTPS with insecure HTTP requests.

Modern browsers block HTTP content loaded from HTTPS pages.