In order to know why did the user not receive a message on messenger, you will have to do certain troubleshooting. This includes:

Ensuring you have commented with your personal profile and not the page.

Ensure you have given all permission

Go in page settings and ensure you have allow people to message page privately.

Ensure your Page messenger is connected properly in the jumper dashboard; try reconnect or disconnect and re-connect Fb if you continue to face an issue.

Lastly some user/buyer may have added privacy setting to stop anyone from sending them a private message

Alternatively the user/buyer profile may also be marked by fb for spam or may not be verified yet by fb (this usually happens for new accounts created which are otherwise not active fb users)

Ensure you have connected your payment gateway and set the ways you want to receive payments.

If any of the above persists, then the user may not receive a message.