Multisite multiple domains and wp-signup.php

Hi everyone. Forgive me if this question is stupid, but I’m still quite new to WP MS.

I have a WP MS install using subdomains on a server that has (at the moment) no “real” domains pointing at it. I have instead edited my host file to mimic the use of the domains, while I’m building the site, as my client have their current site using the domains I need to set up.

I have built the site using morso.co.uk as it’s primary domain and this works fine (as you would expect). However the current site my client has uses morsoe.co.uk as it’s primary domain (notice the ‘e’ in there). They are going to change the primary domain over to the one without the ‘e’ like I have done. They will therefore require morsoe.co.uk to be a parked domain on the new site.

The issue I’m finding is when I come to this setup I’m getting the /wp-signup.php as I’m guessing it can’t find the blog. This also happens for the 301 reirects.

What do I need to do in order to get…

https://www.morsoe.co.uk/some-page.aspx

to become

https://morso.co.uk/some-page/

?

I have looked at using define( ‘NOBLOGREDIRECT’, ‘%siteurl%’ ); but this just redirects to the home page and I don’t think this will be best for SEO.