Custom domains are not a property of your API Gateway project. They sit on top of all API Gateway projects. This means that the same domain with different base paths can point to multiple API Gateway projects. CloudFormation does not support changing the base path from an empty value to a non-empty value or vice versa.
RFC 7118 WebSocket as a Transport for SIP January 2014 5.3.Via "received" Parameter The following is stated in [RFC3261], Section 18.2.1, "Receiving Requests": When the server transport receives a request over any transport, it MUST examine the value of the "sent-by" parameter in the top Via header field value.