Think this issue of Amazon ELB. According [RFC7540](https://tools.ietf.org/html/rfc7540#section-8.1.3) examples server must return HTTP protocol version same as request. * Request ``` POST /resource HTTP/1.1 ``` Responce must be ``` HTTP/1.1 200 OK ``` Amazon returns ``` HTTP/2 200 ``` Wrong version and `OK` is not present. I will close ticket.