Find or create a link
Open the booking in your calendar. The link shows in the Online meeting section, with a note that it has been sent to the customer, and a Copy button to copy it. It also shows on the customer's manage-booking page.
Booking reminder and rescheduled booking emails for an online appointment also include an Online meeting section after the booking details, with the link and a Join online meeting button, once the link exists.
Once the appointment has finished, the link is no longer shown on the booking or on the customer's manage-booking page.
Links are normally created for you. If creating the link failed repeatedly, the booking shows a Create link now button so you can try again. Until then the booking says the link is being created, and you can select Refresh to check again.
If the customer can't be emailed
If the customer has no email address, or has email notifications switched off, the meeting is still created but the customer isn't emailed or reminded. The booking tells you the link needs to be sent to them manually, so use Copy and send it yourself.
Moving and cancelling bookings
If you move a booking, or change when it ends, for example by lengthening a service, the meeting is updated to match within a minute. The link stays the same, and the provider tells the customer about the new time. Cancelling a booking deletes the meeting, the provider tells the customer, and the link is no longer shown. A booking that is later set back to confirmed doesn't get a new meeting.
For recurring bookings, each appointment has its own meeting. Moving or cancelling one appointment only changes that appointment's meeting.