Admin page returns 403 Forbidden; new install

[jacob.salmela]

It looks like your still on dnsmasq v2.72 and Pi-hole v3.3 so it doesn't seem you followed either of these solutions (from the link @mibere posted):

How do I revert to a previous version of Pi-hole?

if you want to run a different version of Pi-hole, it is possible to install an older version. Typically, we release all three components of Pi-hole at the same time (Core, Web, and FTL), so you'll usually want to install version from the same "release." For example, we ran into some issues with v3.3 and dnsmasq compatibility with some systems, so some users needed to revert to v3.2.1 (Core and Web) but as part of the 3.2.1 "release," the latest version of FTL was 2.13.2. Because we version e…

Install a more recent dnsmasq on Raspbian Jessie

Update: 2018-08-06 As of v4.0, Pi-hole ships with _FTL_DNS, our fork of dnsmasq, which should restore compatibility with Raspbian Jessie. We still recommend installing a newer OS as Jessie is EOL anyway. Please note that this tutorial is only meant for Rasbian Jessie, although it might (to some extend) also help with similar issues on other Debian versions. Do this at your own risk (however, the likeliness of a failure is rather small in our opinion). First step: Download more recent versio…

Why can't I run Pi-hole v3.3+ on Raspbian Jessie or with dnsmasq < v2.72?

Update: 2018-08-06 As of v4.0, Pi-hole ships with _FTL_DNS, our fork of dnsmasq, which should restore compatibility with Raspbian Jessie. We still recommend installing a newer OS as Jessie is EOL anyway. By default, Raspbian Jessie only supports dnsmasq v2.72, which does not work with the log-queries=extra flag, which is required for Pi-hole v3.3+. You may see error messages such as: dnsmasq: extraneous parameter at line 37 of /etc/dnsmasq.d/01-pihole.conf failed! There are two option…