Follow these steps to renew your 3CX SSL certificate (assuming that the PBX in question is SP0 as the last contact with 3CX servers has been made from a 15.5 SP0 – In this case the system must be updated to the latest service pack)
To force the update:
- If version is lower than v15.5 SP2 skip this step:
- Starting from v15.5 SP2, go in Settings / Parameters:
- Set or Add TEMPORARY_SELF_SIGNED_CERTIFICATE_GENERATED and give it value of 1.
- Log in via SSH.
- Type: /usr/lib/3cxpbx/PbxConfigTool -renew-certificates
I got the instruction above official from 3CX Support Helpdesk.