How do I set open_basedir correctly

I have kanboard on a server where Kimai sets open_basedir in the nginx config, like this

 fastcgi_param PHP_ADMIN_VALUE "open_basedir=$document_root/..:/tmp/";

This causes permission errors like this one

Unable to open primary script: /var/www/kanboard/index.php (Operation not permitted)" while reading response header from upstream, client: 127.0.0.1, server: domain.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/usr/local/php7/var/run/php-fpm.sock:", host: "domain.com:8060"

The kimai server is on another port (80)

Is there any way to deal with this?