Kong Regex In Uri

Hi i have 2services that i want to share same Domain…the difference is if user go to “www.domain.com” should redirect to my Landings Service but if user add anything after the domain itself like “www.domain.com/[UserName]” user should redirect to My DashBoard Service…for that i used a Regex in Uri for the Dashboard Service like below:
/(?=(.[a-z0-9]){3}+)(?=(^((?!static|js|css).)$))
all it say is the username should be at least 3 characters or numbers and url should not contain any js or css or static words in it…
now when i save this changes it dosent work and always redirect user to DashBoard Service even if user enters “www.domain.com” and nothing after it…

i dont know how to make it work!

P.s: the uri for the Landings Service is just a “/”
P.s2: if i empty the browser cache and try “www.domain.com” it sends a request to “/css/main.css” and redirects to My Landings wich is what i want but if i refresh, it goes to dashboard again!