Aliexpress
Click here… to search for Amazfit Stratos 3 Smart Watch on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in Hong Kong. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood.
Link: Banggood product page
Price: -3 USD
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Old coupons (from the oldest to the newest): BGAS3199, bgwp, BGAS3198, BGNAAFS3, BGAMZ200, BGAM3EN, amazfit100, BGABS3, BGAS3192, 7d18f7, BGA3CU, BGA3174, BGAM35, BGAS179, BGAS174, AS136, BGDQAS3, BGILAF3, BGAS139, BGPowerstation, BGAS134, BGZBAS3, BG11AS3, Email5, BGAFAMS, BGAS3U, BGBFSTR3, BGAS3BF, BGBRAS3, BGFabioamaz, 6GSGIT, BG3a5e6d
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for Amazfit Stratos 3 Smart Watch.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).