You’re doing the whole thing in a wrong way. First of all you should not redirect the domain to ftp server url.
You should point your domain using A record or Nameservers. Whatever option you have/works for you.
And then change siteurl and home url in your database with the new domain name. More Details about this process
And then use a plugin like Velvet blues update urls to replace old url’s with new domain’s url.
After doing these, your site should work fine.