You can leave the voucher activation module unchecked, that way your users will only see a login and password field, where they can enter the same code. This will activate the code and logs the user in as well.
Click modify hotspot data and settings – VOUCHERS / ACCESS CODES and uncheck the box next to activation module.
You can further simplify the login process by turning off the password field, using the “Simplified Login (password only):” option. This way there will only be 1 field displayed in the splash page.
Click manage-locations-modify hotspot data & settings – splash page sttings and check the box next to: Simplified Login (password only
Note: The voucher activation module is used only to activate a voucher, not for logging in.