That won’t work. See post #12 above (http://forum.mikrotik.com/t/a-very-simple-redirect-to-an-http-page-after-join-wifi/165960/1).
DHCP Option 114 is critically different from Option 160. Option 160 does allow a URL to redirect, but I’m not actually sure what/if anything support it. Apple does not look for Option 160, only Option 114 (with HTTPS+JSON returned).
Reason is the DHCP Option 114 spec (RFC-7710) requires it returns JSON, with the URL to visit on the device embedded in the JSON returned. The JSON with URL could be a static file on a web server, anyplace – but it has to be from a HTTPS site with valid certificate. Mikrotik doesn’t easily let you just server web pages (WITHOUT using /ip/hotspot) — so need a web server, someplace, is needed to use Option 114. And needs web server MUST have a valid SSL cert for a device to use the URL (e.g. andriod and apple will only show the captive portal if web uses https:// NOT http://).
So for an ISP, they likely have a billing system, which likely has a secure web server to use to serve the JSON needed to “warn” as user – assuming preexisting config that use Option 114 in CPEs to check a URL in a billing system’s web server. While not 100%, likely be useful to direct a customer who hasn’t paid what to do…
For a home user, curious admin, or small office…Option 114 is trickier since you need a web server. Since OP seem to be using NodeRED (see my example above) – that has a web server and runs in a Mikrotik container, but you need something like that use Option 114… But any web server, like ngnix or apache, can work too.
And /ip/hotspot will also work with Option 114. Here the Mikrotik would need to have a valid certificate in the /ip/hotspot setting. The Mikrotik docs talk about Option 114 here… See: https://help.mikrotik.com/docs/pages/viewpage.action?pageId=56459266#HotSpot(Captiveportal)-UsingDHCPoptiontoadvertiseHotSpotURL