role_type is in boost/beast/core/role.hpp (API Change):

This enumeration is now part of the library core and
not specific to websocket.

example/websocket/server/async-ssl/websocket_server_async_ssl.cpp

@@ -87,7 +87,7 @@ public:
         // Set suggested timeout settings for the websocket
         ws_.set_option(
             websocket::stream_base::suggested_settings(
-                websocket::role_type::server));
+                beast::role_type::server));
 
         // Set a decorator to change the Server of the handshake
         ws_.set_option(websocket::stream_base::decorator(