Voicemail does not work
From Kolmisoft Wiki
VoiceMail application is missing
Make sure VoiceMail application is loaded:
CLI> show modules like mail Module Description Use Count app_hasnewvoicemail.so Indicator for whether a voice mailbox ha 0 app_voicemail.so Comedian Mail (Voicemail System) 0 2 modules loaded
If it is not, restart Asterisk and look for error messages.
Fix error or recompile Asterisk.
External server is checked
Go to SETTINGS - Billing - DIDs - PBX Functions - VoiceMail and uncheck (if checked) VoiceMail Server active.
If Voicemail starts to work, it means that you misconfigured External Voicemail server (or clicked this checkbox by accident).