Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (137.44 USD): BGCCARG
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): BGXiaomiSmart, BGAFF10OFF, BgoFErTaSchInA10, 7bcdf9, BgcLuBofErtA10, BG20CHARGER, BGMBCBLE, BGCuponation10, BGHXMWCT, BGHONEY2110, BANGGOODSD
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Xiaomi 20W Smart Tracking Wireless Charger is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).