Mailbox for PJSIP channels isn't properly defined

AsteriskNOW with FreePBX is installed and the FreePBX initial setup is completed. A PJSIP extension is created with voicemail and a Linksys PAP2 is then configured correctly.

A message is left by dialing the phone extension and the message waiting indicator (MWI) does not activate.

Upon moving the line mailboxes=6004@default from pjsip.aor.conf where FreePBX creates it to pjsip.endpoint.conf and issuing the command rasterisk -x "core reload" the MWI activates, and deactivates once the message is deleted.