what I am doing wrong (DDNS)

[ttbf_n]

First, I enabled DDNS with asus.com and it worked, created a certificate and all good for a while, then it started intermittently not resolving my ip. Pinging my hostname said unresolved, so probably asus did not return anything at all.

Then, I have registered dynu.com which I know works well (tested with terminal commands on Mac).
Custom inadyn.conf in /jffs/:

custom dynu {
ddns-server = api.dynu.com
ddns-path = "/nic/update?username=%%h&myip=%%i"&password=%%p"
hostname = xxxxxx.dynu.net
username = xxxxxx
password = "md5_hash_of_password"
}
verified with inadyn --check-config -f "/jffs/inadyn.conf"
Then added ddns-start script from documentation and gave it execute permissions.
After applying, log shows no obvious errors, but apparently retries until time out, but dynu.com appears never actually reached:

May 27 15:04:02 watchdog: start ddns.
May 27 15:04:02 ddns: update CUSTOM , wan_unit 0
May 27 15:04:02 ddns: Clear ddns cache.
May 27 15:04:02 custom_script: Running /jffs/scripts/ddns-start (args: my_ip)

and this repeats 5 times, then again 5 times after ~30 minutes or so. I do not see any errors, but no updates at dynu.com. Router shows "registration successful" which I do not understand why.

Any help appreciated, probably I have done something stupid. Thanks.