Server response when Content-Type is not present

Clients MUST send all JSON:API data in request documents with the header Content-Type: application/vnd.api+json without any media type parameters.

I couldn’t find in specification what should server do when receives request without Content-Type header. Could you please help me clarify?

For me, I think it will be okay to respond the client with 415 http status code.

https://httpstatuses.com/415

Thoughts?

Agreed, that is the HTTP standard.