I get this 404 error: how do i fix it?

You check that the information you put in is correct. If it is, contact the people running the site, or the creator of the application you're using.

KiltedTim: Server errors typically have a number starting with a 5, not a 4.

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The 4xx and 5xx HTTP status codes are both issued by the server. However, the 4xx are classified as errors likely caused by the client, and 5xx as those indicating server problems. See List of HTTP status codes.

That's a server error. You can't do anything to fix it.

404 is page not found. It's issued by the server.