WifiClient vs WifiServer

I'm building a wifi server. At first printing to the WifiClient worked fine when it needs an HTML page. But then it stopped working. After a few days of hair pulling, I printed to WifiServer instead and the HTML page finally showed up on the browser. What's going on here?

And also, can I set an IP to the server? I know you can do it to the Ethernet library but there's nothing on the WiFi library.