When I was updating this page, then coupon price was $15.99 for SONOFF MINIR4M MINI Extreme WiFi Smart Home Switch (in Banggood). You can create price alert here, copy coupons and view price history. Do you want to know what the best price is?
SONOFF MINIR4M MINI Extreme WiFi Smart Home Switch Detach Relay Matter Voice Control with Alexa Google Home
Latest coupon code price check (UTC time):
Banggood ($15.99)
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. Is it cheap? This price is higher than average price ($14.84) for this item.
Link: Banggood product page
Price: $15.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Check out price history chart (for all/most countries) for SONOFF MINIR4M MINI Extreme WiFi Smart Home Switch.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).