HI. I migrated my old version 4.5 to the lastest V5 I kept the same subdomain for my new V5 and I had some issues with my URL but I figured out chancguin a value on my DB. Regarding redirecting old mail URL I just add a couple of lines to my .htaccess on /public
Redirect OLD v4 URL
RedirectMatch 301 ^/view/(.*)$ https://MYDOMAIN/client/invoice/$1
RedirectMatch 301 ^/payment/(.*)$ https://MYDOMAIN/client/payments
Hopefully this help someone out there.