It's not always possible to set up passive checks correctly the first time. In such cases, it is a good thing to try to debug the issue one step at a time in order to find any potential problems. Sometimes the problem could be a configuration issue, while in other cases, it could be an issue such as the mistyping of the host or service name.

One thing worth checking is whether the Web UI shows changes after you have sent the passive result check. If it doesn't, then at some point, things are not working correctly.

The first thing you should start with is enabling the logging of external commands and passive checks. To do this, make sure that the following values are enabled in the main Nagios configuration file:

log_external_commands=1
log_passive_checks=1

In order for the changes to take effect, a restart of the Nagios process is needed. After this has been done, Nagios will log all commands passed via the command pipe and log all of the passive check results...