There is a drop down box in the dynamic dns page
2 options
Dyndns.org
No-ip.com
Domain Name
User name
Password
Check box to enable DDNS
I tried putting api.dynu.com as domain
My user name and pwd but connection is not getting made

Kindly advise

Dynu is not integrated in your device at this time. You may use free IP update client software. However, we suggest that you take a few minutes to comment on the manufacturer's support forum requesting that Dynu be added to the dynamic DNS service provider list to make your life easier.

Hello Jesse Markx,

Did you ever get any support from TP-Link to update their firmware and add support for "custom" dDNS service providers? My router model is a TL-WDR4300.

Hi everyone! Well it's October 2019 and TP-Link has still not changed the options. Is there any way to work around this or can the update client do the job fine without configuring the router with my dynu account?

The IP update client alone is enough to keep the IP update. You do not need to set up the router if you use the client.