In this guide, we’ll explain the most common REST API errors, what they mean, and how to troubleshoot them effectively using best practices. Whether you're facing a "500 Internal Server Error", a "create-order API failed" issue, or simply wondering why your "API works locally but not on the server", this article is your go-to resource.
Table of Contents
An API error is a failure in communication between systems via an Application Programming Interface (API). It may occur due to incorrect requests, server issues, authentication failures, or unexpected runtime problems.
When an API is "not reachable" or an "API hit failed", it can signal connectivity issues, authentication errors, or broken endpoints. Knowing how to troubleshoot API issues starts with understanding the nature of these errors.
HTTP status codes are a critical signal when an API fails. They reveal whether the issue lies with the request itself, authentication, the requested resource, or internal server errors. Below is a breakdown of the most common error codes you'll encounter while troubleshooting REST APIs — and how to resolve them.
Meaning: The server couldn’t process your request because the syntax was incorrect or essential information was missing.
Common causes:
application/json)Fix:
Check your API documentation and ensure all required fields are present. Use tools like Postman or curl to validate your request. Logging your request payload can also help pinpoint the exact issue. When developers search "how to fix an API error", this is often the culprit.
Meaning: The request was denied because proper authentication credentials were missing or invalid.
Common causes:
Fix:
Ensure you’re sending a valid token or API key, typically in the Authorization header. If you're using OAuth, make sure the token hasn’t expired. Refresh tokens, where applicable. Many API not working scenarios are simply authentication problems in disguise.
Meaning: You are authenticated, but your user doesn’t have permission to access the requested resource.
Common causes:
Fix:
Review your user permissions and roles. In some APIs, you may need additional scopes or privileges. This is especially relevant when troubleshooting errors like bio auth API error or social attribute API error, which rely heavily on secure permission structures.
Meaning: The server couldn’t find the requested endpoint. This is one of the most frequent REST API errors.
Common causes:
Fix:
Verify that the endpoint path is correct and matches what’s defined in your API documentation. Double-check for typos and case sensitivity. This is a key area in API 404 error troubleshooting, especially in microservices, where routes may change frequently.
Meaning: A general error indicating that something went wrong on the server side.
Common causes:
Fix:
Check your server logs and application monitoring tools. Look for stack traces and debug output to locate the issue. This error often appears during API crash scenarios or when the create-order API failed. Implement robust error handling to prevent unhandled exceptions from causing system-wide outages.
Meaning: These errors signal issues with upstream servers, load balancers, or network timeouts. The API request hit the server but didn't make it through the entire service stack.
Common causes:
Fix:
Retry the request using exponential backoff strategies. Monitor the availability of your backend services. These errors are a common source of API connectivity issues and are often temporary. Tools like Datadog or Pingdom can help track server health in real-time.
Meaning: These less common errors can cause major disruptions when they appear.
Fix:
For 507, check your disk space, temporary file directories, and memory usage—especially important in cloud environments. For 508, ensure your logic doesn’t create circular dependencies or redirects. These errors usually arise in advanced API runtime scenarios and can cause serious performance issues.
Your application is trying to reach the API, but nothing happens. This might be due to misconfigured routes, environment issues, or missing dependencies.
How to fix it: Review server logs for startup errors, verify your base URL, and ensure all services are running as expected.
When the API can’t be reached at all, you may be facing DNS resolution issues, SSL problems, or firewall rules that block traffic.
How to fix it: Run a curl or ping test, verify SSL certificates, and check DNS records or IP whitelists.
You receive a response, but it’s an error, often due to invalid payloads or expired authentication tokens.
How to fix it: Inspect the full request (headers, body) and retry with updated values. Use Postman to test authentication flows.
This specific business function fails, often due to backend validation or third-party integration issues (e.g. payment).
How to fix it: Confirm all required fields are sent, check the state of inventory and payment status, and inspect downstream responses.
Biometric authentication calls fail, which could mean mismatched data, outdated SDKs, or timing issues.
How to fix it: Sync timestamp data, validate the biometric hash format, and make sure the SDK version matches backend expectations.
Sudden failures may happen due to unhandled exceptions or poor memory management.
How to fix it: Review crash logs and use observability tools to monitor resource usage. Add try/catch blocks and stress test critical endpoints.
Classic issue—your code runs fine locally but breaks in staging or production.
How to fix it: Double-check environment variables, ensure correct base URLs, and verify network restrictions like IP filtering and CORS policies.
You’re sure the endpoint exists, but the API returns “not found.”
How to fix it: Validate the URL path and method. Ensure you’re targeting the correct versioned route and check for typos or casing issues.
Issues occur while fetching user profile data from social logins.
How to fix it: Make sure access tokens include the right scopes and that your app is approved to use the social provider’s extended attributes.
Debugging and resolving REST API issues can be a challenging task for developers and API development companies. However, various tools and methods are available to help you troubleshoot and resolve REST API issues.
Let’s have a look at some of the best tools available:
Once you’ve identified an API error — whether it’s a 500 response, a timeout, or a failed endpoint — the next step is to handle it in a way that prevents future failures and improves developer experience. These API troubleshooting best practices will help you create more resilient, debuggable, and maintainable APIs.
From logging strategies to graceful fallbacks, here’s how to troubleshoot API issues effectively and avoid them in the future.
Detailed logs are your most powerful tool when investigating what caused an API failure message. Always log:
Structured logging (e.g. in JSON) makes it easier to filter by error types or endpoints during analysis.
Avoid vague messages like "Something went wrong". Instead, return meaningful error objects that include:
This helps users quickly understand what an API error meaning is — reducing support tickets and speeding up debugging.
If a request fails due to invalid tokens or insufficient scopes, your API should:
Poor handling here is one of the leading causes of recurring API not working reports, especially in OAuth or session-based systems.
Temporary issues — such as 500, 502, or 503 responses — should trigger automatic retries on the client side.
Best practice:
This is essential when addressing API connectivity issues or load-based timeouts.
APIs can appear healthy but still fail under pressure. Use Application Performance Monitoring (APM) and health checks to track:
Tools like Prometheus, Grafana, or Datadog give real-time insights into API runtime health and help detect issues before users report them.
Don’t let bad data reach your core logic. Use validation layers (e.g. JSON schema, Joi, or middleware) to reject malformed requests upfront.
This reduces the chance of logic-level bugs and improves your API’s ability to return precise 400 Bad Request errors.
Many API failure cases are due to misconfigured security. Follow these minimum rules:
Bonus: Protect against brute-force and abuse with rate limiting (e.g. 429 Too Many Requests).
Your API documentation should clearly list:
Good docs save hours of troubleshooting. If someone searches “what is an API error?”, your docs should be their first stop.
Backwards-incompatible changes are a frequent source of API request failed incidents.
Best practice:
/v1/orders, /v2/users)This avoids confusion and breakdowns when consumers hit old routes unknowingly.
Use automated tests to simulate:
Tools like Postman, SoapUI, or custom test suites help ensure you’ve covered all failure points, especially in scenarios like “API works locally but not on server” or “create-order API failed”.
By following these best practices for API error handling, you don’t just solve problems—you prevent them. A well-monitored, secure, and gracefully failing API leads to faster development, fewer support tickets, and a better user experience.
Troubleshooting REST API issues can be a challenging task for developers. However, it doesn’t have to be too difficult with the right strategies in place. This section will explore some of the top tips for troubleshooting REST API issues.
Troubleshooting REST API issues doesn’t have to be frustrating. By combining structured analysis, proven tools, and best practices, developers can resolve most issues quickly and avoid them entirely in the future.
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