redis-server3.service: Can't open PID file /run/redis/redis-server3.pid (yet?) after start: Operation not permitted code example

Example: redis-server.service: Can't open PID file /run/redis/redis-server.pid (yet?) after start: Operation not permitted

[Service]
Type=forking
ExecStart=/usr/bin/redis-server /etc/redis/redis.conf
ExecStop=/bin/kill -s TERM $MAINPID
ExecStartPost=/bin/sh -c "echo $MAINPID > /var/run/redis/redis.pid"
PIDFile=/run/redis/redis-server.pid