Hi All,
I have configured Synology router using the instructions from dynu.com
The Custom ddns option is not available by default so I have followed the following instruction: and used the given query

[Dynu.com] 
modulepath=DynDNS 
queryurl=api.dynu.com/nic/update?hostname=__HOSTNAME__&username=__USERNAME__&myip=__MYIP__&password=__PASSWORD__

It looks like it is working as shown in the screenshot
Sorry, the screenshot I uploaded to imgbb does not seem to be working.
There is a green Normal shown in the Network Centre >> QuickConnect & DDNS section
However, when I try to connect to the router by using the registered domain nothing happens.

Is there anyone out there who succeeded in setting up Dynu.com ddns on Synology rt2600ac?

Thanks,
Rafal

Looks like you are using a .eu domain name. Did you list the following Dynu name servers for your domain name at your domain registrar:

ns1.dynu.com
ns2.dynu.com
ns3.dynu.com
ns4.dynu.com
ns5.dynu.com
ns6.dynu.com

Hi Timothy,
Thank you so much for pointing this out.
The registrar is godaddy.com and I have found the option to set custom Nameservers.
The original name servers used were

ns07.domaincontrol.com	
ns08.domaincontrol.com	

Which I have replaced with

ns1.dynu.com	
ns2.dynu.com	
ns3.dynu.com	
ns4.dynu.com	
ns5.dynu.com	
ns6.dynu.com

For each nameserver there is an option to add an IP address but I have left these blank as the original ones were also unfilled.

Unfortunately this still did not work.

This site can’t be reached
XXXXXXXX.eu took too long to respond.

I have tried clearing cookies from the browser and using private mode as cache and cookies have been a problem for me in the past in another case regarding ddns. (I think)
After a few more minutes (maybe 10) I got through and it looks like it is working.

Thank you Timothy!

EDIT: I am not out of the woods yet. Not everything is working fine but I will keep trying and update this post with some more information.

But still, Timothy, your post was very helpful. Thank you!