@Yveaux Thanks, it helped me.

@masmat No it's not necessary to put the "Contact" in a sitemap, your arduino shall send boolean (0/1).

@MagnusF - if the error is a bad bootloader, but that is rarely the case... I have seen that once. It will not hurt though to re-upload the bootloader if you suspect thats the problem.

Higher security if you have incoming connections from outside your Lan and more flexibility if you have other devices accessing data directly on mqtt, but if you are running just your simple setup there is no real need

@MagnusF clever use of the adapter. I like it :)