Matomo no external visitors

Hello everyone,

we are using Matomo in combination with a drupal website.
So we have following network.
internet -> web application firewall -> Drupal website (Apache) -> Matomo (Apache).

The Apache is only the webserver for the content, so there is no proxy usage.
Because of the waf, there is only the internal ip adress of the waf visible.

Unfortunately we don’t see the visitors, who are connection over the internet.
Otherwise we are see the users who connect to the Drupal website directly (internal).

We are using Matomo 3.6.
The server ist not accessable from the internet and has noch connection to the internet.

What could be the problem?