Direct link is working for the HSR website! Click on the code for the direct link if you don’t want to copy-paste manually. Make sure to log in with your HoYoverse account.
Here is the official redemption code website: https://hsr.hoyoverse.com/gift?code
But before that, copy the code below (or just tap on the code to automatically fill the prompt box):
Rewards: Stellar Jades x50 & Credits x10000
It is unknown when the redemption codes above will expire (Most probably after 1.5 update).