This sounds more like a keyboard hardware or connection problem than a typical Bluetooth pairing issue.
Try these steps:
- Charge the keyboard fully
- Connect it to power via USB cable for at least 30 minutes.
- If possible, try a different USB cable and charger.
- Connect it to power via USB cable for at least 30 minutes.
- Power-cycle the keyboard
- Turn the keyboard off.
- Wait 30 seconds.
- Turn it back on and test several keys.
- Wait 30 seconds.
- Turn the keyboard off.
- Test it on another computer
- This is the most important test.
- If the same keys fail on another Windows PC or Surface, the problem is almost certainly with the keyboard itself.
- This is the most important test.
- Remove and re-pair via Bluetooth
- On your Surface, go to Settings → Bluetooth & devices.
- Remove the existing Surface Keyboard entry.
- Restart the Surface.
- Try pairing again.
- Restart the Surface.
- Remove the existing Surface Keyboard entry.
- On your Surface, go to Settings → Bluetooth & devices.
- Important in your case: the pairing-code problem
- Normally, Windows displays a PIN/code that you type on the keyboard and confirm with Enter.
- Since almost all keys are unresponsive, don't keep trying to fix this through Bluetooth settings — if the keyboard can't register the required digits, pairing simply can't complete that way.
- Testing on another computer is therefore the best way to tell a pairing issue apart from a hardware failure.
- Since almost all keys are unresponsive, don't keep trying to fix this through Bluetooth settings — if the keyboard can't register the required digits, pairing simply can't complete that way.
- Normally, Windows displays a PIN/code that you type on the keyboard and confirm with Enter.
If only the "9" key works
If you've already charged the keyboard fully and "9" is the only key producing a response, I wouldn't recommend opening the keyboard or attempting a repair. This pattern strongly points to an internal keyboard matrix or controller failure.
Since Model 1742 is less than a year old, you should pursue Microsoft's warranty/support process rather than buying a replacement keyboard.