Temporary msg for a site

I have a request to pop a msg of decommission for a site before going to the actual site

I am trying the solution https://devcentral.f5.com/questions/irule-to-pop-up-a-window-then-continue-to-page

Can anyone help me with the error I am getting TCL error: /Common/Ciphers-Test-iRule - Operation not supported. Multiple redirect/respond invocations not allowed (line 2) invoked from within "HTTP::respond 200 content { //DTD XHTML 1.0 Transitional; ";