IIRC, the Sling Adapter was for the ViP722, maybe for the Hopper 2000 and was discontinued in 2019 because it used technology that was easily hacked (Adobe Flash) and was in the hardware - therefore not fixable.
This Satellite Guys discussion in 2017 is still not clear whether the Sling Adapter worked on the Wally. Wally and Dish Anywhere