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 (15.29 USD): band10
Coupon (15.29 USD): BGCuponation10
Coupon (15.99 USD): 13f142
(CouponsFromChina.com tip: paste coupon code in your cart and click Apply 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): 15M20, 14m20, 12M20, 11m20, 502C6B, BG15D, 9M20, TTxBG10, BG9M20, AFfbG10, BGBK15, BGBFAFF2019, BGBAK15, BGAFF10OFF, bgshOOp10, BG11SHOP
(probably won’t work, but you can try them out)
Price history and price alert
Check out price history chart (for all/most countries) for Bakeey M20 Smartwatch Black.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).