Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (8.81 USD): Sports23q1
Coupon (9.20 USD): BG589b2e
(CouponsFromChina.com tip: just apply this code in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BG8377e3, Cuponation9, BG00c906, BG98b565, BG4682dc
(probably won’t work, but you can try them out)
Price history and price alert
Here is price history (for all/most countries) for Back Support Straight Posture Corrector.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).