credentials are wrong, there is no way to redo it without accessing the ext4 root partition on an external system or attaching a keyboard, which is no possible as the on micro USB port is used for power supply and the other one by the WiFi adapter.

I see it’s a bid nasty if WiFi on RPi Zero failed, and a reboot (plug off, plug on) does not solve it, e.g. The dietpi-wifi.txt template however shows that pretty fine. Use single quotes at best, since they won’t expand $ as variables and such. In dietpi-wifi.txt quotes are required if you use special characters or spaces in SSID or password, since it is sourced, hence treated as it’s content is “executed” in the shell. In dietpi.txt btw quotes btw must not be used, since it’s content is parsed via sed/grep. Bringing up that interface failed as wpa_supplicant failed, so the interface in fact was present (else wpa_supplicant wouldn’t have been invoked), but credentials were wrong or wpa_supplicant failed for a different reason.

As long as it’s Zero and not Zero W, the interface will be wlan0.

Pi zero w headless setup