A Passcode is used to unlock the device when you turn it on. A Passcode can be numeric or alphanumeric.
The screen unlock passcode which can be 4 digits, 6 digits, Custom
length numeric, or a custom length alphanumeric passcode is still
called a passcode, not a password.
If its asking for a numeric only passcode, it means you had a numeric only passcode on the other device to unlock your device. If you had an custom alphanumeric passcode to unlock your device, then it should have provided a full keyboard to enter it.
Your Apple ID password or login password for your email is not what is being asked for.
Is it maybe asking you to create a passcode?