openhab does not officially support http/get to trigger items, only htp/post.
In case you cannot use http/post I suggest the following options:
-
official way
use this binding
this binding is not released. You have to install it yourself. I am also using it and it just works great -
inofficial way
use this http/get request:
openhab:8080/basicui/CMD?item=command
You have to install BasicUI and be aware that this hack may be dropped any time without any prior notice as it is an unsupported feature are a feature used for something elase but to trigger items from 3rd party devices.