Thank you for providing more information and screenshots related to this issue.
Could you please confirm if you are using the same current admin password that you use to connect to the router’s WebUI, or are you using the default password found on the sticker on the back of the device? You should use the current admin password, which is the one you changed when connecting to the device’s WebUI for the first time. Additionally, please enable remote HTTP access by going to System → Administration → Access Control; this shouldn’t make any significant changes.
If that doesn’t resolve the issue, I recommend factory resetting the device and starting the connection steps from the beginning.
If you don’t remember the current admin password, you’ll need to perform a factory reset by pressing and holding the reset button for at least 14 seconds.
Once reset, connect to the router’s WebUI, change the password to something you’ll remember, and enable remote HTTP/HTTPS access.
After that, you can start the process of connecting the device to the RutOS app from the beginning. Keep in mind that after the reset IP address of the device will be default –192.168.1.1.