Cannot configure NAT-Instance properly (No route to host)

Summary:

I tried to configure a NAT-Instance (public subnet) and a DB-Server (private subnet) according to this https:ording//docs.oracle.com/en-us/iaas/Content/Resources/Assets/whitepapers/nat-instance-configuration.pdf Paper, but my DB-Server is still not able to connect fully to the internet.

Content (required):

Running the ping command to a public server works fine but a HTTP/HTTPS request gives me the error No route to host.

I do not know to to debug a network call or where the issue can be. I am thankful for any help.

Version (include the version you are using, if applicable):