HTTP 431 Request Header Fields Too Large Error

Root of the issue

The total size of the request headers exceeds the server's limit.
A single header field's size is too large.
The Referer URL included in the header is excessively long.
The request includes too many cookies, increasing the header size beyond acceptable limits.

# Request example 
curl -X GET https://sandbox.oxylabs.io/ -H 'Accept: text/html' -H 'Accept-Encoding: gzip, deflate' -H 'User-Agent: Mozilla/5.0'

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Check the server's response for the "Upgrade" header to identify the required protocol.
Modify the client's request to support the protocol specified by the server's "Upgrade" header.
Ensure that the client and server both support the upgraded protocol.
Restart the client application to apply the new protocol settings and retry the request.

# Response example 
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: text/html; charset=UTF-8
Content-Length: 49

431 - Headers Too Large

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From

401 Unauthorized	403 Forbidden	404 Not found	405 Method not allowed	406 Not acceptable
407 Proxy authentication required	408 Request timeout	409 Conflict	410 Gone	411 Length required
412 Precondition failed	413 Payload too large	414 Uri too long	415 Unsupported media type	416 Range not satisfiable
417 Expectation failed	421 Misdirected request	422 Unprocessable entity	423 Locked	424 Failed dependency
426 Upgrade required	428 Precondition required	429 Too many requests	431 Request header fields too large	444 Connection: close
451 Unavailable for legal reasons	499 Client closed request	501 Not implemented	503 Service unavailable	505 Http version not supported
506 Variant also negotiates	507 Insufficient storage	508 Loop detected	510 Not extended	511 Network authentication required