I use a raspberry pi with the dynudns update.
It works well to connect and update, but it ONLY updates the ipv6 address, never the ipv4 address.
But if I connect with other devices (like my Android phone), they can't connect because they use the old ipv4 address that I don't get updated.

What is wrong?
I followed https://www.dynu.com/DynamicDNS/IPUpdateClient/RaspberryPi-Dynamic-DNS
And use this url to update: https://api.dynu.com/nic/update?username=USERNAME&password=PASSWORD

So I can see that the ipv6 gets updated (and if I change it to something else, after an update it is OK), but the ipv4 always stays the same; even if it is wrong (when I manually change it; the respons is always "nochng")

thank you

By using this update URL https://api.dynu.com/nic/update?username=USERNAME&password=PASSWORD, the server will pick up the IP address from where the update request originates. I guess only IPv6 was detected so only IPv6 was updated.

If there is any way you can get the IP address first and then use the IP address in the update string, both IPv4 and IPv6 will be updated:

https://api.dynu.com/nic/update?username=USERNAME&password=PASSWORD&myipv4=IPv4&myipv6=IPv6

Someone familiar with raspberry pi could write up a script to do it.

Posting the solution for completeness' sake. This is the full command:

echo url="https://api.dynu.com/nic/update?username=USERNAME&password=PASSWORD&myipv4=$(curl -s -4 ifconfig.co)" | curl -k -o /path/to/logfile -K -

If you need your IPv6 address as well you can append to the url:

&myipv6=$(curl -s -6 ifconfig.co)