Run -
cat /etc/samba/smbpasswd
And make sure your user and password are present, it should look something like -
cbx200:1000:xxxxxxxxxxxxxxx:B233GYHH78JHH
If it's not present try making it again with -
smbpasswd -a
Default masks should be 0777, but it wouldn't hurt to set them manually just to make sure, you can always change them when you have samba working
Also, remove this line from you samba template as it's not needed -
valid users = kuku, luisa
Here's my working template so you can check yours against it -
[global]
netbios name = |NAME|
display charset = |CHARSET|
interfaces = |INTERFACES|
server string = |DESCRIPTION|
unix charset = |CHARSET|
workgroup = |WORKGROUP|
bind interfaces only = yes
deadtime = 30
enable core files = no
invalid users = root
local master = no
map to guest = Bad User
max protocol = SMB2
min receivefile size = 16384
null passwords = yes
passdb backend = smbpasswd
security = user
smb passwd file = /etc/samba/smbpasswd
use sendfile = yes