DNS settings for the second-level domain.

Hello everyone,
Can you please help me with DNS settings?

We have www pages on the Internet on the domain contoso.com. If I enter www.contoso.com in the browser, the browser is redirected to contoso.com (the page are then, for example, https://contoso.com/about.html). This works for me at home and on my mobile, but it does not work on the local network, where it says that the page is unavailable + DNS_PROBE_FINISHED_NXDOMAIN.

In my opinion, this is caused by the DNS settings, which do not return any IP address when querying contoso.com.

I have a USG FLEX 500 and in System / DNS / Address / PTR record I have some third-level domains set up, for example (ftp.contoso.com or code.contoso.com) and I point them to private IP addresses.

All computers on the local network use DNS in the USG.
If I try to ping contoso.com from a computer on the local network, it says "Ping request could not find host contoso.com".
If I run an NSLookup test for contoso.com in the USG in Maintenance / Diagnostics / Network tool, it does not return any IP address.

If I remove all third-level domains that have contoso.com in the second-level domain from DNS in the USG, the query for contoso.com returns the correct IP address and the www pages work on the local network as well.

What should I set so that DNS from the USG correctly returns the IP address for the second-level domain contoso.com?