Can only leave voicemail when making internal calls

I have Freepbx 16.0.40.11 and have a pretty basic setup with 2 sip trunks from Flowroute. I have 4 internal extensions pjsip lines. I’ve turned on voicemail, but I can only leave voicemail when making calls between extensions. If I call in externally over the sip trunks, I can’t leave a VM. Instead I just see this error message: [2024-11-16 00:35:36] VERBOSE[22030][C-00000025] app_voicemail.c: Recording was 0 seconds long but needs to be at least 1 - abandoning.

I’ve got the min VM length set to 1 second and even if I try and leave a really log VM externally it still sayes the recording was zero seconds long.

I’ve tried making new extensions that are voicemail only (not connected to any hardware) and still no dice.

Any suggestions?

Are you able to receive PSTN calls to one of your 4 internal extensions with two-way audio ?