I see that the virtual remote you choose is not working properly. You can try a similar model and see if that works.
Below are some helpful links with additional troubleshooting steps;
- My remote control is grayed out or doesn't work
- SlingPlayer displays the wrong onscreen remote control. How do I fix it?
Sling Media Support Team
If you are going to recommend these links you need to get them updated. Both refer to watch.com for re-configuring the input and that is no longer possible, you have to use the Desktop app. Also the first one was obviously written years ago when all Slingboxes used the external IR blaster. That is also not necessarily the case these days and will confuse owners of newer boxes.