[VLESS-TCP-XTLS-Vision-REALITY] Why do some websites return a 406 Not Acceptable error when using the proxy?

[eone-5in]

I have been using the config from VLESS-TCP-XTLS-Vision-REALITY.

Everything works fine, but some websites fail under the proxy. Can anyone help me adjust the configuration or explain this behavior?

Example: https://developers.giphy.com/
— clicking “Create account” returns a 302 HTTP status without the proxy, but a 406 error with the proxy.
The site uses Kong API Gateway, which seems to block my requests.

What I’ve tried:

1. Various curl requests with different headers — still 406.
2. Different fingerprints and site-camouflages — still 406.
3. Using a SOCKS and TProxy — still 406.

Any insights on the cause?

P.S. The Medium app also fails under the proxy; likely the same issue.