If you've enabled the setting Setup > Security > Party Passcodes, you can choose to share this passcode by email invitation.
Simply, include the code directly in your invitation using the available merge tag.
Where you place this tag, RSVPify will automatically insert each party's respective code.
Instead, you can also enable 'Skip welcome screen and password; send guests directly to Step 2'. With this setting enabled, the system will automatically authenticate and identify the guest, and the guest will be directly to Step 2 to select their reply and answer any additional questions you've included.