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 (285.65 USD): hoNEYbGdeAlS
(CouponsFromChina.com tip: apply it in your 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): BGLEM18922, BGLEM15, BGSWATCH10, BGLEM153, BGLEM1503, BGNTHMA, BG4a5413, BGa522cd, 6GSGIT, BG621c0f, BG20e3b6, BGcbe03d, BGBF1117, BG9c79c5, BG029716, BG51f436, ADMITAD2212, BG1efce1, BGLEM15FANS, BG2202FANS18, 2203ActiesNL, BGfbdb26, MVC8SPRING, BG0a8381, pROMo8cuPoN
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for LEMFO LEM15 4/128GB Smart Watch.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).