Why can't I book a match with someone I know is a club member?

This can happen in a number of circumstances. Matches take place in the context of an event like leagues, tournaments or friendlies. For the former two, matches are preset and your opponent may have decided to leave the tournament. For friendlies, too, your opponent may be injured and has decided to retire for a while.

But in all cases, the most common issue is that the person concerned has an unpaid court fee. Generally, fees are charged to a member's club account when the service is used. If the member does not have enough money in their account, then they are messaged and asked to replenish their club account. In the mean time they are prevented from booking further courts. Furthermore, other people are prevented from booking a court with them.

In summary, the first thing to check when you seem not to be given the choice of a member with whom to book a court, ask them if they are due to top up their account.