The Plesk default page or 404 errors are shown on the site example.com
IP address 203.0.113.2 assigned to the website example.com in Domains > example.com.
The domain example.com resolves globally to another IP address:
# dig example.com
;; ANSWER SECTION:
example.com. 86400 IN A 203.0.113.3
If DNS is managed by Plesk, set correct A record in Domains > example.com > DNS Settings.
If external DNS server is used, change the A record on external dns server side.