How to solve “rDNS is NOT forward confirmed” and “x.x.x.x.in-addr.arpa looks like generic” errors

when testing the reverse forward DNS using a tool, I got this:

FCrDNS test result:
x.x.x.x resolved to x.x.x.x.in-addr.arpa;
x.x.x.x.in-addr.arpa unresolved;
rDNS is NOT forward confirmed.

Generic PTR record test result: x.x.x.x.in-addr.arpa looks like generic.

With other tool, I got this:

Reverse DNS to x.x.x.x

IP address: x.x.x.x Reverse DNS: OK x.x.x.x.in-addr.arpa
Reverse DNS Authenticity: Warn Could be forged: Hostname
‘x.x.x.x.in-addr.arpa’ does not exist Reverse DNS
Domain: x.x.x.x.in-addr.arpa

Can you give me some hints about how to correct them?

I manage both the host computer and the DNS server, which are different machines.