My wi-fi bridge on RT-AC51U fails (unable to create socket on ...)

I have a problem with establishing a wi-fi bridge on my I followed the guide at which seems to be working at least till the testing connection part. However, there seems to be missing part about how to actually set up a wi-fi network on the repeater. So I tried to set up an access point as usual, but when the connection is created, I can't connect to it, getting error messages such as

bind(21) AF_INET6 fe80::6b42:32ff:2b68:9197%3#123 flags 0x11 failed: Cannot assign requested address
unable to create socket on wlp3s0 (5) for fe80::6b42:32ff:2b68:9197%3#123

on my (Linux Mint) laptop and

Wed Mar  8 06:23:46 2023 daemon.notice wpa_supplicant[1255]: wlan1: Unknown event 37

in the system log of OpenWRT (22.03.2 r19803-9a599fee93).

So my questions are:

  • How should I configure my access point on the bridging router (RT-AC51U)?
  • How can I make sure that my relay bridge is correctly configured?

Thanks in advance

It looks like these messages may not be relevant, as I'm seeing them also during successful connection to the wi-fi.