HTTP 417 Expectation Failed means the server cannot meet the expectation specified in the request's Expect header. This most commonly occurs when a server does not support the Expect: 100-continue mechanism.
The client sent Expect: 100-continue but the server or proxy does not support interim responses.
Send the request without the Expect header.
curl -H 'Expect:' -X POST -d @file.dat https://example.com/upload
Some proxies strip or reject the Expect header. Test against the origin directly to isolate the issue.