This is not a chat model and thus not supported in the v1/chat/completions endpoint. Did you mean to use v1/completions?
Welcome to the forum,
Does your account have gpt-4 API enabled? This can happen if you attempt to modify the hyperlink text to force the GPT-4 model when it is not enabled on your account.
It could also be a transient issue with the API/Playground and it would be worth retesting in an hour.