nuober of process of mariadb

Hi all, i just try to create a new alert that check the number of process of a specific systemd service: i use this collector:

and this specific data set systemd.service.pids.current, i set the alert so that it is triggered when the number of processes in the service goes below a certain number.
I have done several tests but it does not activate in any way, the rest of the created alerts work fine, but this one seems not to be active.
in that data set there are several dimensions, each of which represents a systemd service, I wonder if it is correct to indicate the service being examined by passing it in the lookup?
like this:

...
lookup: average -1m unaligned of nginx
...

do you have any segregation? thx