The SlimmeLezer comes preconfigured with ESPHome, so it can added to Home Assistant quite easily.
The best way for setting it up, is to power it via an USB power supply. In some minor cases, when the SlimmeLezer starts broadcasting its own AP ‘slimmelezer’, it may draw a little too much power and can give problems during setup.
When it’s powered up, it broadcasts a wireless network ‘slimmelezer’. Be patience as this can take 20 to 40-ish seconds. Connect to that wireless network with a phone, tablet or laptop. Once connected, a captive portal will show after some seconds (10 seconds on my iPhone SE and 40 seconds on my iPhone 11 Pro). There you select your network and fill in the required password if needed. Note: hidden networks do work, yet needs an extra setting which isn’t set in my precompiled firmware: fast_connect: true).
When it takes too long to show the slash page, got with a browser to the ip-address http://192.168.4.1
Once connected, it will auto discover in Home Assistant, where you can complete the integration.
If it doesn’t appears in the auto discovery, go to Add Integration > ESPHome:
That’s it, you’re all set to use the SlimmeLezer.