I think I was pretty clear in the other thread:
This is most likely because your Raspbian is outdated, for example, if you’ve created your SD card from the pre-configured SD card image of OSPi (several years ago), that Raspbian is unfortunately outdated and does not support the IPv6 feature in the current firmware. The solution is to burn a new Raspbian system using the latest Raspbian image from RPi website, and then follow instructions here to install OpenSprinkler firmware:
https://openthings.freshdesk.com/solution/articles/5000631599-installing-and-updating-the-unified-firmware
If you don’t want to install new Raspbian, you can also roll back to an earlier firmware, but next time there is a firmware update you will encounter the same issue again, so it’s better to just solve it now.