Got Grav running great in my Linux, PHP7, Nginx space and can do everything fine except save theme settings. Just updated to latest build and all plugins as well with no change. Double checked file permissions as well. Using Grav v1.1.12 and Admin v1.2.7
Using Nginx conf supplied and no errors being logged.
Turned debug on and attached results.
@mahagr looks like a gantry5 issue?
My bad... I now see that the appearance menu is specific to gantry themes.
Same as https://github.com/gantry/gantry5/issues/1748
I'm really not sure what could cause this to fail in Nginx as we just call
$nonce = Utils::getNonce('gantry-admin');
and
protected function checkSecurityToken()
{
/** @var Request $request */
$request = $this->container['request'];
$nonce = $request->get->get('nonce');
return isset($nonce) && Utils::verifyNonce($nonce, 'gantry-admin');
}
Same as https://github.com/getgrav/grav-plugin-admin/issues/893 using g5_hydrogren

Replicated
Please update nginx.conf:
location / {
try_files $uri $uri/ /index.php?_url=$uri&$query_string;
}
Works like a charm now! Thanks
Not nginx.conf but well the configuration of the site in sites-available
Most helpful comment
Please update nginx.conf: