Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (12.59 USD): BG9d995e
Coupon (15.63 USD): BGAUDIO
Coupon (15.63 USD): BG9ba0e8
(CouponsFromChina.com tip: you should apply the coupon 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): BG5fa8b5
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Xiaomi Capsule DDQ01WM Earphones 3.5mm.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).