Aliexpress
Click here… to search for Xiaomi Redmi K20 Pro 6/128GB Black on 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 (368.99 USD): BGBFAFF2019
Coupon (368.99 USD): BGCITYADS2019
Coupon (381.29 USD): od7off
(CouponsFromChina.com tip: apply code in your basket (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): BG7K20P2, aff7off
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for Xiaomi Redmi K20 Pro 6/128GB Black is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).