Cannot customise website after updating permalinks.

Hello,

I recently started working on a wordpress project that is being hosted by a third party. I changed the permalinks to the domain name that I wanted to use and updated my .htaccess file according to instructions. My site displays perfectly fine on the new domain.

However, since updating the permalinks I can no longer use the customise tool. When I do so, the frame doesn’t show my website and instead shows a login screen (yet curiously I’m not logged out). When I try to log in it accepts, but then automatically redirects me to log in another time (stating my login expired). The whole time I remain logged in, accessing this window through the customise tool.

I assume the permalinks are the issue here as this worked fine before I changed them. For note, when I go to customise my site, my address bar will read:

my_original_server_name/wp-admin/customize.php?

Wheras my actual website is: https://www.mytestinggrounds.top

Not sure if that is related, though.

I’m comfortable with advanced coding, so any advice (technical or not) is greatly appreciated!