Check login.html file
If your Captive portal is opening incorrectly, Similar to the picture below. You need to check your login.html file.
login.html file is located under Files section in Winbox. Find your login.html file and make sure that it is located inside Hotspot folder. Same as pictured below.
Also worth noting is that the size of login.html file should be around 858 B (shown in the picture above). If the size of your file is varying by a lot, check that you have successfully created your login.html file. You can re-download it from here.
NOTE: If you are having trouble downloading the file, copy it's contents to text editor and save the new file as login.html yourself.
Check Walled Garden configuration
If you get the error "Webpage not available" or similar, when trying to connect to your network, check Walled Garden settings.
In Winbox, go to IP -> Hotspot -> Walled Garden and check that both "logme2wifi" and "spotipo" are there and they have action "allow" listed.
If the action is set as deny, double click on the denied host and set the status to allow. Press ok to save changes.
If any of these hosts are missing, you can add them by clicking New Terminal to open the Terminal Window in Winbox. After that, run commands below.
/ip hotspot walled-garden
add dst-host=*logme2wifi*
add dst-host=*spotipo*
Captive portal stuck on loading screen after authentication
If you get this error, a separate article is available here.