Aliexpress
Click here… to search for Xiaomi ZMI QB822 20000mAh Power Bank on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
Coupon (37.19 USD): aff7off
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply after clicking “Proceed to checkout”. Click to copy code and open shop)
Old coupons (from the oldest to the newest): BG3CSUM, BGPAYPALSS, BGaDmITAd, BGBFAFF2019, BGCITYADS2019, 2020CNY, BGVDay10%off
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi ZMI QB822 20000mAh Power Bank.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).