Side-sleeping backpack, L size

Purchased but unused.
Selling because I no longer have the opportunity to use it.
Quoted from the HP below:
Purchase price: 8,000 yen

This product helps you quickly develop the habit of sleeping on your side so that your tongue, soft palate, and relaxed throat tissues do not fall backward and block your airway. It helps reduce snoring caused by throat problems.
It is large enough to prevent you from turning onto your back at night, so you won't lie on your back or strain your spine like you would with a small or rigid supporter. You can adjust the air capacity of the airbag to find the most suitable sleeping position. If you would like a free airbag replacement within the 3-month warranty period, please send us a message.
This backpack features a 3-point fixation between the shoulders and waist, so it will not shift or slip over time. Please note that we ship two versions of buckle straps and touch fastener straps randomly.
Size Guide - There are two sizes available. Measure the width of your back between your armpits, but do not include your arms. The large size is for people with a back width of 16 inches (40 cm) or more. We recommend people of medium build choose the large size backpack.