The Stellar Blade Bar 99 chest code is something that you won't come across until much later in the game, long after finding the chest itself which means some backtracking is needed. Found in Eidos 7, the Tetrastar Chest with the broken, red keypad seems useless since you can't even enter numbers to try and brute-force the passcode.
So how exactly do you get it open? In short, it's tied to story progress, but you also need to engage with the game's side quests to learn the passcode, at which point you can go back and open the red chest which now miraculously works. I've explained exactly how to open the red Tetrastar chest in Stellar Blade, as well as what's inside
How to open the red keypad chest in Bar 99 in Stellar Blade
The red Tetrastar chest in Eidos 7's Bar 99 in Stellar Blade cannot be opened the first time you encounter it - in fact, you won't be able to open it until much later in the game, returning to that area hours later.
To open it, you need to progress the story until you reach a location called Xion, which has a Bulletin Board. The board has a list of optional secondary missions and challenges that players can take on for extra rewards, with more missions becoming available as you progress through the main story.
After you complete a story mission called Light of Hope, head back to the Bulletin Board to see an optional mission called Legion's Lost Stash (expect this point to be roughly 8-15 hours in, depending on ability and how much optional content you're doing).
This mission simply gives you the passcode for the red Tetrastar chest in Bar 99 on Silent Street Eidos 7: 1228. Not only that, it actually unlocks the ability to enter the passcode in the first place: until then, you are simply denied at the keypad.
If you need help finding the chest again, head to Eidos 7 and, from the landing point, follow the street until you reach the section where you have to swing on bars over the chasm. Progress straight on, but watch your left side for a flickering sign that says Bar 99. Go through the door beneath it (there'll be a couple of enemies) and follow the path to the left side to find the red chest.
Opening the chest will get you a variety of nondescript Nano Elements of various types, including some Extreme-quality Elements for improving Eve's nanospine.
This is how the red consoled-chests work, ultimately - they're contextual. You'll find more throughout the game, and simply have to come back to them when a mission or document gives you the code.
You can pick up lots of other side missions through the Bulletin Board, such as the Stellar Blade simple puzzle and Stellar Blade wisdom puzzle, both of which give you Gold as a reward.
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