Aliexpress
Click here… to search for Oneplus 6T 8/256GB Midnight Black on Aliexpress
Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in Hong Kong. You can get coupon down below.
Link: Banggood product page
Coupon (718.82 USD): affiliate6
(CouponsFromChina.com tip: coupon code has to be applied in shop’s 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): 11BG6T256, plfonall
(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 Oneplus 6T 8/256GB Midnight Black.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).