Writing the current proces pid to cgroups.procs fails with permission denied error – CentOS

I am trying to write a pid to a manually created cgroup but I am unable to do so.

While writing, I am getting the following error:

open /sys/fs/cgroup/pids/scratch-container-cgroup0049cba7-8f9e-42ec-9646-9b1babbfebc3/cgroups.procs: permission denied

The file has the following permissions:

[~~]$ ls -l cgroup.procs
-rw-r--r-- 1 root root 0 Feb 14 23:27 cgroup.procs
[~~]$

The code that I am using to write it as follows in Go

    procs := filepath.Join(containerCgroupPath, "cgroups.procs")
    currentPid := strconv.Itoa(os.Getpid())
    log.Printf("current pid is %s", currentPid)
    if err := ioutil.WriteFile(procs, []byte(currentPid), 0777); err != nil {
        return err
    }

However, using bash also gives out the same error.

sudo echo "100" > cgroup.procs 
bash: cgroup.procs: Permission denied

I am not sure what I am missing about cgroups here that could be used to write. I am on Centos that is running systemd.

I am able to write to pids.max and notify_on_release

I will really appreciate insights here.