The Nuki Keypad 2 is listed as supporting up to 200 codes (not beyond). Examples on how to create codes via the Web API are listed here: Web API Example: Manage PIN-Codes for your Nuki Keypad (Your keypad will need to be paired with the lock, the lock will need Internet access, and you will need to ensure your PIN codes are unique, …)
Of course, you could always drive the lock from your own server, either via the Web or other API, and then have whatever UI/keypad attached to that that you want. Could be a button in your app, a keypad, a camera/barcode scanner looking for a QR code that the user presents them, … (I do this with my Nuki Opener.)
All that said, I’m not sure using a lock to turn a key is the best option for you. (You might want to consider an access solution with an electromagnetic lock, or an electric strike that would allow your staff to use keys but guests to be buzzed in, …)