A pay-per-view message is a message with content your fans pay to unlock. They can be big earners on OnlyFans. They are available to all the creators on OnlyFans.
You can send PPV messages to your subscribers and these messages are price locked so your fans can only view it if they pay.
If you are new to OnlyFans then PPV messages will be activated after 2 days of verification. Then only you can send messages to others. So wait for 2 more day then try again.
Other reason may be you have violated some policies of OnlyFans so OnlyFans has blocked you from send PPV messages.