An SSP represents the seller (the app) in programmatic advertising, connecting inventory to demand-side platforms and exchanges. In mobile gaming, much of that role is bundled into mediation platforms and the large vertically integrated networks.
Adding another SSP is a common reflex when revenue softens. It can help for specific geo or format gaps, but in most mobile games revenue flows through a few primary pipes, and the bigger lever is usually in the product: pacing, reward design and retention.