Samba error in dfree command

On my OpenSUSE Leap 15.3 with Samba version 4.13.4, I have a test share in a btrfs subvolume with 1GB quota, with the following config:

[global]
        workgroup = HOME
        passdb backend = tdbsam
        printing = cups
        printcap name = cups
        printcap cache time = 750
        cups options = raw
        guest account = smbguest
        map to guest = Bad User
        logon path = \\%L\profiles\.msprofile
        logon home = \\%L\%U\.9xprofile
        logon drive = P:
        usershare allow guests = No
        netbios name = server
        wins support = No
        dfree command = /usr/local/bin/df_btrfs
        dfree cache time = 1
        log level = 10

[test]
        comment = test
        inherit acls = Yes
        path = /srv/samba/test
        read only = No
        valid users = test
        vfs objects = snapper btrfs
        force user = test
        veto files = /.snapshots

Everything works correctly, except the disk usage. It displays the full disk usage and ignores the quota, so I used the following script and passed it to the dfree command = option.

df_btrfs:

#!/bin/sh

# Not very efficient but its a draft
btrfs quota rescan -w $1 > /dev/null
STR=$(btrfs qgroup show -rF --raw $1 | tail -1)

NUM1=$(echo $STR | cut -d " " -f 4)
NUM2=$(echo $STR | cut -d " " -f 2)

SIZE=$(expr $NUM1 / 1024)
USED=$(expr $NUM2 / 1024)
AVAIL=$(expr $SIZE - $USED)

echo $SIZE $AVAIL

And when I execute grep "df_btrfs" /var/log/samba/log.smbd this is the output of the logs:

  server:/usr/local/bin # grep "df_btrfs" /var/log/samba/log.smbd
     doing parameter dfree command = /usr/local/bin/df_btrfs
     doing parameter dfree command = /usr/local/bin/df_btrfs
     sys_disk_free: Running command '/usr/local/bin/df_btrfs .'
     sys_popenv: ERROR executing command '/usr/local/bin/df_btrfs': Permission denied
     sys_disk_free: file_lines_load() failed for command '/usr/local/bin/df_btrfs .'. Error was : No child processes

But these are my scripts permissions:

server:/usr/local/bin # ll
   total 4
   -rwx------ 1 root root 269 Aug 30 18:07 df_btrfs

What am I missing here? According to the manual the permissions are set up correctly.

Every bit of help is greatly appreciated. Thanks in advance!