Can you point me to the Bitnami documentation that you have followed? I would like to verify is up-to-date.
I see a misconfiguration in your apache files. You are configuring invoiceninja using a prefix (see the file INSTALLDIR/apache2/conf/bitnami/bitnami-apps-prefix.conf) and also using a virtual host (see the file INSTALLDIR/apache2/conf/bitnami/bitnami-apps-vhosts.conf). You should only configure it one way or another.
Also, in the file INSTALLDIR/apps/invoiceninja/conf you set:
while I think it should be: