Aliexpress
Here are coupons that you can use.
Latest coupon code price check (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!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BGOP9R256D, 13f142, BG9R1227, BG048b16, BG5061b3, BGOP9R256725, BG20eae8, BG392bb0, BG582304, BG3d69cb, BG72b51b, BG37d264, BGd55031, BGbb264b, BG187746, BG5b4cdf, BG5a4f62, BGefdc99, BG56ad07, BGc99d64
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for OnePlus 9R 5G 12/256GB Global ROM is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).