Unable to connect to Home Assistant (even though instance is found, worked before)

Hi all
I apologize if this has been answered already, cannot find it.

Running HA on a Rpi4, 6-7 Zwave devices, works OK. Running latest OS and HA (updated 1st June 2020). Beginning to learn it all.

Previously, I could connect to the instance using the Android app when on same wifi as Rpi is is (Rpi cabled to router). Have tried deleting the App, reinstalling it.

Now, the instance is found in the App (Name of instance / http://IP-address:8123). But, I just get this error in the App:
Unable to connect to HA. Please check connection settings and try again. Have checked that I have both default config and mobile config in configuration.yaml.

Could it simply be the IP-address that is wrong? How do I check the IP to use from inside the HA GUI? (Which is all I use, Samba worked before, now it does not, no idea why, insufficient skills to troubleshoot)

Hoping you have ideas. Thank you.

You would find the ip address of your ha box in your router (ip tables). If you haven’t already, it would be a good idea to give your ha box a fixed ip so it can’t move around.

Thank you @micque. Yes, just had to find the hassio IP by logging in to the router. Then, the App works.
I will search for ways to give the Rpi4 a fixed IP.
Thanks from a noob.

The easiest way to give it a fixed address is through the router. There should be a way based on the mac address to lock the ip. You should really lock the ip addresses of all the devices your connecting into your home automation. Makes the system more robust and stable. Do you have to? No, but you already had a taste of things moving around. Good luck.

Was this after the os update?

I assume you mean the inability of the App to connect to the HA instance. This occured before the OS update. I have no way of knowing, but seeing as it now works - with the correction of the IP address - I guess that was the cause.