What do I do if players serve, receive or play at the wrong end out of order?

You control the order of serving, receiving and ends and correct any errors (ITTF Statutes 2026, regulation 3.3.2.3.5; Law 2.14):

• Wrong server or receiver: interrupt play as soon as the error is discovered. Resume with the players who should be serving and receiving at the score reached, following the sequence set at the start of the match and, in doubles, the serving order chosen by the pair with the right to serve first in the game where the error was found.
• Ends not changed when they should have been: interrupt play as soon as it's discovered and resume with the players at the correct ends at the score reached.
• All points scored before the error was discovered count.

Reminders of when changes are due (Law 2.13):

• Serve passes after every 2 points; from 10-all, or under the expedite system, after every point.
• Ends change after each game, and in the last possible game when either side first scores 5 points.
• In the last possible game of a doubles match, the pair due to receive next changes its receiving order when either pair first scores 5 points.

Correcting an error is one of the reasons you may interrupt play (Law 2.9.2.1); the interrupted rally is a let.