Hi,
A couple of things you could look into:
* Can you not only see the target as UP on /targets, but also see the "up" metric for the exporter job when querying for it? If not, maybe the system time between your Prometheus backend and your browser frontend is off, although modern versions of Prometheus should show a warning about that in the web UI.
* What does the "scrape_samples_scraped" metric say about the number of samples scraped from the Apache exporter job?
* What does the "apache_up" metric say, in case it exists?
Cheers,
Julius