If you have the Deposit Collection Non Payment Booking Status setting set to Cancel non paid bookings, New bookings will have the status canceled until we receive IPN notification from Paypal that the payment succeeded. Notification emails confirming the booking will also only be sent once IPN notification of a successful payment is received.
Note: If the booking page is used within an Iframe or in wordpress it cannot redirect the user to PayPal due to the security settings in browsers. To fix you can allow the the paypal page to open in a new window.
Go to SETTINGS -> BOOKING PAGE -> PAGE DESIGN -> ADVANCED and set Open in New Window to On secure payment