It is very unusual for a camera partnership to give up on the cash like this - if it goes to court, they do not get the money it goes to central funds.
I can only presume that they have already laid information with the court and that he will get a summons shortly - it can take 3 - 4 weeks.
In court, the Mags will probably slightly increase the fine and the CPS will ask for costs of about £35 - this amount will be on the summons.
One question - if they have rejected the payment, where is his licence? It should have been sent with the payment and he
will need it for court
BTW, if this is Gwent constabulary, they have a history of getting the paperwork wrong for the court. Try
PePiPoo: Helping the motorist to get justice for help in how to fight the summons. Whilst, morally he may be culpable; the law has to be followed by them as well in order to prosecute successfully.