RSYNC ERROR 4

The DNS name is a local resolution (I am using OpenWrt router)...

The error looks to be only shown when trying the job from GUI ReadNas, but the job also look to complete...

on the ReadyNas :

$ ps aux
root 19061 27.8 0.9 17196 5012 ? RN 13:06 0:42 rsync -vP -8 --timeout=1800 --recursive --links --times --omit-dir-times --devices --specials --ignore-times --one-file-system --owner --group --no-acls --no-perms --port=873 /tmp/19024/EBOOKS user2@10.4.2.102::share2/EBOOKS/

on the OpenWrt NAS client :

$ tail /var/log/rsyncd.log
2021/04/01 13:06:23 [23456] connect from GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 13:06:23 [23456] rsync allowed access on module share2 from GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 11:06:23 [23456] rsync to share2/EBOOKS/ from user2@GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 11:06:23 [23456] rsync: ACLs are not supported on this server
2021/04/01 11:06:23 [23456] rsync error: requested action not supported (code 4) at clientserver.c(1098) [Receiver=3.2.3]
2021/04/01 13:06:24 [23457] connect from GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 13:06:24 [23457] rsync allowed access on module share2 from GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 11:06:24 [23457] rsync to share2/EBOOKS/ from user2@GDISK.lpm.nddc.gk2.net (10.4.2.25)
2021/04/01 11:06:24 [23457] receiving file list
2021/04/01 11:38:42 [23457] sent 19978620 bytes received 12183841 bytes total size 26229514080

$ top
23458 23457 nobody R 13716 3% 42% /usr/bin/rsync --daemon --no-detach
23457 2053 nobody R 6116 1% 40% /usr/bin/rsync --daemon --no-detach

For reference :

https://forum.openwrt.org/t/solved-rsyncd-error-4/92026

Thanks all for your advices and help !