We have had a number of inquiries from people that have purchased the Onyx Ballistic Sling Bag regarding attaching and using the O-Slide sternum stabilizer strap.
The strap attaches easily to the shoulder strap as shown in the instructions that come in the accessory package. Simply pull a loop of the main strap through the o-ring and then feed the sternum strap back through it. See picture --->
Once installed it can be adjusted and worn as shown in the picture below. Based on your questions we are designing better instructions to include in the packs. Thank you for bringing this to our attention and thank you also for the compliments we have been receiving on these new packs!