SOLVED: Can't connect to server

[en33-08]

I'm not sure to be honest. I have this following setting on my router's page, "Automatically control WLAN devices between the 2.4 and 5 GHz frequency bands and between multiple FRITZ! products in the mesh - This function is designed to improve data transmission and requires the same WLAN network name (SSID) on both WLAN frequency bands of the FRITZ!Box or the mesh repeater." (translated via Google Translate), which makes it sound like that 2.4 GHz and 5 GHz devices should be able to communicate with each other but they clearly didn't. I can't really find any other setting that mentions anything regarding this type of thing.