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 (281.99 USD): BG589b2e
Coupon (281.99 USD): BGProjcc
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): BGWBT44, BGProj, BGWBNT44, BG6bf7cb, BGaeeda5, BGc58258, BG22f913, BGNCK649, BGFoxby11, BG99914d
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Here is price history (for all/most countries) for Wanbo T4 WIFI6 Android Projector 1080P.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).