A booking can be cancelled automatically because not enough players joined, by the club, or by the lead booker. You get a push notification and an email in each case.
Not enough players joined
Matches and activities can have a minimum number of players. If too few join by the club's deadline, the session is cancelled automatically. You get a full refund to your original payment method. See "What happens if my match or activity is cancelled automatically?".
The club cancelled it
The email says "your booking has been cancelled by the club". The club decides whether you get a full, part or no refund. Contact the club if you have questions.
The lead booker cancelled it
If the person who booked the court cancels, the whole booking is cancelled. You get back at least the same percentage as they did under the club's rules.
Good to know
If your payment failed during checkout, the booking wasn't made. See "Why was my payment declined?".
Find the payment for a cancelled booking under Profile → Purchases, filtered by Refunded or Cancelled.