Great job! I’m glad to see the UK/EU users are finally getting to enjoy the community developed SmartApps!
Edit: note that if you are using the thing state plugin, the %st_attr_value should already be set. Adding in the Thing: Get Attribute will result in a slight delay as SharpTools has to query SmartThings for the attribute value even though it just received it with the push event.
Have you checked out the link to the example I posted? The example shows how to subscribe to a Thing/Attribute in SharpTools and then react whenever that attribute changes in Tasker.
It looks like the approach @Lind_Lau_el_Loren is taking is to use the Media Control action in Tasker to simulate a Play and Pause button press. I would start with getting that running (assuming the media app is already open)… and once you get that setup, we can work on making sure the app is opened in case it isn’t already open.