Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in Hong Kong. Well, there is one coupon available right now.
Link: Banggood product page
Coupon (399.99 USD): BG3b9eb1
(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): BG4d8318, 00c906, BG00c906, BGef96eb, BGaf4993, BG973af4, BG8671c0, BGbf5460, BG25d295, Kortings10, 2022ACTIESNL, BGc62c8f, BG3d9222, BG8936c6, Cuponation9, 9OFFSUMMER, BG4d956c, BgGoodie9, BG265501, BG3cf2b2, BG16646e, BG0bf87e
(there’s a little possibility that old coupon will work)
Price history and price alert
Check out price history chart (for all/most countries) for Minisforum HM50 Ryzen 5 4500U 16/512GB Mini PC.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).