After I got token I used miiocli yeelight --ip 192.168.x.x --token <token> set_developer_mode 1
to set developer mode on. After that I just used latest Mi Home app to add bulb to my wifi. Developer mode was still set to on and finally I could add it to Home Assistant
Did you try to turn on dev mode again? I think that token should be the same after you pair device with Mi Home app. Token is auth for api and it should be the same. Just you have to change IP to new IP which the bulb will get after you pair it to your home network.
I add it to HA via gui. Integrations, add integration and select Yeelight. In popup I added ip address of my bulb and that was that. Ha connected to my bulb.
I was using this command. It is almost same as yours.
miiocli yeelight --ip 10.21.91.214 --token <my_token> set_developer_mode 1`
WARNING:miio.device:Found an unsupported model 'yeelink.light.mono6' for class 'Yeelight'. If this is working for you, please open an issue at https://github.com/rytilahti/python-miio/
WARNING:miio.integrations.light.yeelight.spec_helper:Unknown model yeelink.light.mono6, please open an issue and supply features for this light. Returning generic information.
Setting developer mode to True