Error Fixes & Troubleshooting

HTTP 502 Bad Gateway Explained

Learn how HTTP 502 errors occur when upstream servers return invalid responses, and how to diagnose reverse proxy and load balancer issues for apps.

HTTP 503 Service Unavailable Explained

Learn to identify and resolve HTTP 503 errors caused by server overload, maintenance windows, or upstream failures in production environments effectively.

HTTP 504 Gateway Timeout Explained

Learn what triggers HTTP 504 errors when upstream servers fail to respond within timeout windows, and how to tune proxy and backend performance settings.

HTTP 429 Too Many Requests Explained

Learn how HTTP 429 enforces rate limiting, interpret Retry-After headers, and implement exponential backoff for resilient API client applications with care.

HTTP 413 Payload Too Large Explained

Learn why HTTP 413 is returned when request body size exceeds server limits, and how to adjust max body sizes in nginx and Apache server configurations.

HTTP 431 Header Too Large Explained

Learn what causes HTTP 431 errors from oversized cookies or headers, and how to increase buffer sizes or optimize client requests for web applications.

HTTP 508 Loop Detected Explained

Learn how HTTP 508 errors occur when infinite request loops are detected in proxy chains, and how to debug redirect loops and configure protective measures.

CSRF Token Mismatch Explained

Learn why CSRF token mismatch errors occur when submitted tokens do not match session tokens, and how to debug token validation in web applications effectively.

CSRF Token Expired Explained

Learn what causes CSRF token expiration when session timeouts invalidate embedded tokens, and how to configure lifetimes and refresh strategies for web apps.

JWT Expired Explained

Learn how JWT expiration errors occur when the exp claim is exceeded, and how to implement refresh token rotation and configure expiration windows in your apps.

JWT Invalid Signature Explained

Learn why JWT invalid signature errors happen when token integrity verification fails, and how to debug key mismatches and algorithm confusion in auth services.

JWT Invalid Issuer Explained

Learn what triggers JWT invalid issuer errors when the iss claim does not match trusted issuers, and how to configure issuer validation across systems.

JWT Invalid Audience Explained

Learn how JWT invalid audience errors occur when the aud claim does not match the intended recipient, and how to restrict audience validation in services.

OAuth Invalid Grant Explained

Learn why OAuth invalid grant errors are returned when codes or refresh tokens are invalid, and how to debug the token exchange flow for better auth.

GraphQL Validation Error Explained

Learn how GraphQL validation errors occur when queries violate schema rules, and how to interpret error paths and fix common query syntax mistakes in APIs.

GraphQL Resolver Error Explained

Learn what causes GraphQL resolver errors when field resolution functions throw exceptions, and how to trace failures and implement error boundaries for apps.

GraphQL Non-Null Violation Explained

Learn how GraphQL non-null violation errors occur when a non-nullable field resolves to null, and how to debug resolver return values and null handling logic.

GraphQL Union Error Explained

Learn why GraphQL union type errors happen when resolvers return types not in the union definition, and how to implement proper type resolution for your APIs.

WebSocket Close Reasons Explained

Learn how WebSocket close codes indicate connection termination reasons from normal closure to protocol errors for building real-time resilient applications.

WebSocket Protocol Error Explained

Learn what causes WebSocket protocol errors when frames violate RFC 6455 specifications, and how to debug masking errors and fragmentation issues in streams.

WebSocket Handshake Failure Explained

Learn why WebSocket handshake failures occur when upgrade requests are rejected by the server, and how to check origin and proxy configurations thoroughly.

gRPC Status Codes Explained

Learn how gRPC status codes communicate RPC outcomes from OK to UNAVAILABLE, and how to interpret error details and map HTTP/2 conditions to gRPC error codes.

gRPC Deadline Exceeded Explained

Learn what triggers gRPC deadline exceeded errors when RPCs take longer than configured timeouts, and how to set appropriate deadlines in your service calls.

gRPC Unauthenticated Explained

Learn how gRPC unauthenticated errors occur when credentials are missing or invalid, and how to configure TLS mutual auth and tokens for secure RPC channels.

gRPC Permission Denied Explained

Learn why gRPC permission denied errors occur when authenticated users lack access rights, and how to implement RBAC and authorization interceptors in gRPC.

gRPC Unimplemented Explained

Learn what causes gRPC unimplemented errors when servers lack handlers for called RPC methods, and how to verify proto registration and method name consistency.

OAuth Invalid Scope Explained

Learn why OAuth invalid scope errors occur when requested permissions exceed granted access, and how to validate scopes and handle incremental auth flows.

OAuth Invalid Client Explained

Learn how OAuth invalid client errors are returned when client credentials are rejected, and how to verify client IDs, secrets, and redirect URIs on servers.

SSL Peer Unverified Explained

Learn what causes SSL peer unverified errors when certificate chain validation fails during TLS handshakes, and how to inspect trust stores and CA configs.

OCSP Revocation Unknown Explained

Learn how OCSP revocation unknown errors occur when responders cannot determine certificate status, and how to configure stapling and validation modes for TLS.

OCSP Stapling Failed Explained

Learn why OCSP stapling fails when servers cannot retrieve signed OCSP responses from CAs, and how to debug stapling configuration in nginx and Apache servers.

SAML Response Invalid Explained

Learn how SAML response validation errors occur when assertions fail signature or condition checks, and how to debug XML signatures and ACS URL configurations.

SAML Issuer Mismatch Explained

Learn what causes SAML issuer mismatch errors when the Issuer element does not match the entity ID, and how to sync metadata between IdP and service providers.

SAML Clock Skew Explained

Learn why SAML clock skew errors occur when time differences invalidate NotBefore conditions, and how to configure tolerance windows and NTP sync on servers.

API Rate Limit Exceeded Explained

Learn how API rate limit errors enforce usage quotas, interpret rate limit headers, and implement retry strategies with exponential backoff for API clients.

DNS NXDOMAIN Explained

Learn what DNS NXDOMAIN errors mean when a queried domain name does not exist, and how to differentiate typo squats from deleted DNS records and configs.

DNS SERVFAIL Explained

Learn how DNS SERVFAIL errors indicate server-side resolution failures, and how to debug authoritative timeouts and DNSSEC validation failures in resolvers.

DNS REFUSED Explained

Learn why DNS REFUSED errors occur when servers decline to answer a query, and how to diagnose ACL restrictions and recursion policy denials on DNS servers.

DNS Timeout Explained

Learn what causes DNS timeout errors when resolvers fail to receive responses within the configured interval, and how to tune timeouts and fallback nameservers.

TCP Connection Refused Explained

Learn how TCP connection refused errors occur when no process is listening on the target port, and how to verify service status and firewall rules for servers.

TCP Connection Reset Explained

Learn what causes TCP connection reset errors when the remote host abruptly closes the connection, and how to identify app crashes using packet capture tools.

TCP Half-Open Explained

Learn how TCP half-open connections occur when one side terminates without completing the handshake, and how to detect orphans and configure keepalive settings.

TCP SYN Flood Explained

Learn how TCP SYN flood attacks exhaust server connection queues with incomplete handshakes, and how to detect and mitigate using SYN cookies and rate limiting.

TLS Handshake Failure Explained

Learn what causes TLS handshake failures when client and server cannot agree on versions or ciphers, and how to debug using the OpenSSL s_client tool.

TLS Certificate Unknown Explained

Learn how TLS certificate unknown errors occur when the CA is not in the trust store, and how to install intermediate certificates and manage CA bundles.

TLS Certificate Expired Explained

Learn why TLS certificate expired errors happen when the certificate validity period has elapsed, and how to automate renewal with Lets Encrypt tools.

TLS Certificate Host Mismatch Explained

Learn what causes TLS host mismatch errors when the server hostname does not match SAN entries, and how to verify certificates and configure SNI headers.

TLS Version Mismatch Explained

Learn how TLS version mismatch errors occur when client and server support disjoint protocol versions, and how to audit and configure version negotiation policies.

TLS Cipher Mismatch Explained

Learn why TLS cipher mismatch errors happen when no shared cipher suite exists between client and server, and how to list and configure secure cipher ordering.

CORS Origin Mismatch Explained

Learn how CORS origin mismatch errors occur when the Origin header does not match allowed origins, and how to configure Access-Control-Allow-Origin headers.

CORS Missing Headers Explained

Learn what causes CORS missing headers errors when servers omit required Access-Control headers, and how to configure proper responses for cross-origin access.

CORS Preflight Failure Explained

Learn why CORS preflight OPTIONS requests fail when servers do not respond with correct headers, and how to configure allow lists and cache responses.

CORS Credentials Not Included Explained

Learn how CORS credentials errors occur when withCredentials is set but Allow-Credentials is missing, and how to enable cookies in cross-origin requests.

API Quota Exceeded Explained

Learn how API quota exceeded errors enforce daily or monthly usage caps, and how to monitor consumption via headers and implement quota-aware throttling.

API Invalid Parameter Explained

Learn what causes API invalid parameter errors when request payloads fail validation, and how to parse error bodies and validate data types and formats.