Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (48.44 USD): BGc70579
Coupon (48.44 USD): BGbf11dd
(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): BG57a2c3, BG9c3757, BG77b838, BGSEAHK8, BG55d6e1
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for HK8 Pro AMOLED NFC Smart Watch is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).