In order to enable the online check-in option go to Property Settings / Online Guest Account / Settings.
1. Click on Enable button.
2. Decide if you want to let the guest:
a) Cancel some nights
b) Cancel only the whole reservation
c) Make online check-in
3. Decide how many days before arrival the guest will be able to peform an online check-in.
4. Decide which fields are required for the booking owner online check-in.
5. Decide if the required fields for the rest of the guests should be the same as in case of booking owner or different. If you uncheck the box you will be able to choose separately the required fields for the other guests.
Don't forget to save the changes!
Please see also:
How to send the information to guests about online check-in?
How to send a reminder to guest about the online check-in?
Where can I see that guest checked-in in the system?
How to enable online check-in for the already existing bookings?