What is “417 expectation failed” Error and How to fix it?

What is the “417 expectation failed” Error?

The “417 Expectation Failed” error is an HTTP status code, indicating that the server couldn’t do what was asked in the ‘Expect’ header of a request.

This error often happens when the server or something in its response process doesn’t support the conditions in the ‘Expect’ header.

Root Cause of “417 expectation failed” Error

As we mentioned, the “417 expectation failed” error usually happens when the server can’t do what was asked in the ‘Expect’ header of a request.

Sometimes, it could be due to specific settings in your application.

For example, if the CorsOrigin parameter in appsettings.json doesn’t end with a forward slash (“/”), this issue might occur.

Here are some possible reasons why this error might occur:

  • Misuse of HTTP methods and headers:

This error often arises when certain HTTP methods and headers, such as GET and POST requests, are used incorrectly.

  • Syntax errors or inappropriate input parameters:

The error can also be triggered by mistakes in the syntax or unsuitable input parameters in the message body.

  • Server’s inability to handle the “Expect” header:

If the server can’t process the “Expect” header field sent by the client, it may return this error.

How to fix the “417 expectation failed” Error?

Here are the solutions to fix the “417 expectation failed” error:

Examine the header:

Use a tool like Fiddler to collect a trace and analyze the header. This can help you pinpoint the problem.

Change the Expect header:

If the server doesn’t support the Expect header field sent by the client, removing this header from the request may solve the issue.

Check your application’s configuration:

Look for any errors in your application’s configuration. For example, make sure the CorsOrigin parameter in appsettings.json ends with a forward slash (“/”).

Turn off the Expect header:

In some cases, you might want to turn off the Expect header.

You can do this by setting System.Net.ServicePointManager.Expect100Continue = false; in your code.


In conclusion, we’ve discussed the “417 Expectation Failed” error.

This error means that the server can’t fulfill what the request is asking for.

While this error isn’t common, it can cause issues for a website and its users when it does occur.

By implementing the solutions provided above, you can confidently address and resolve this issue.

For further learning, you can also check the following HTTP status code:

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