Step 1: Log in to your Charge Automation account then go to Settings > Preferences > PMS Modification.
Step 2: Turn on 'NEW BOOKING RECEIVED' and save.
Step 3: In your BookingAutomation account, you can use:
Template Variable [BOOKINGINFOCODETEXT:CA_PRE_ARRIVAL_LINK]
in your Auto Actions to send to your guests.
NOTE: Only new bookings received after turning ON "New Booking Received" will see the pre check-in link.