Players have unlimited opportunity to challenge, however if three incorrect challenges are made in a set, they cannot challenge again until the next set. If the set goes to a tie break, players are given additional opportunities to challenge.
How the On-Court Player Challenge System Works
Each player is allowed a maximum of three incorrect challenges in a tiebreak set after which they are not permitted to challenge again in that set.
Challenges may not be carried over from one set to another.
In the Advantage set - 5th set for men's singles and 3rd set for women's singles
However, if the match is tied at six games all, the counter is reset with both players again having a limit of up to three incorrect challenges in the next 12 games
Challenges may not be carried over and the process of resetting is repeated after every 12 games
The Chair Umpire will decide to use the Electronic Review when there is doubt by a player about the accuracy of the line call or overrule. The Chair Umpire may refuse the Electronic Review if he/she believes that it is not made in a timely manner and can only be made on point-ending shots or when a player stops play. If the Official Video Review is unavailable for any reason, then the 'original' call will stand.