I believe @ashcortech is correct on the need to update your FPBX 13 setups to use Chan_PJSIP before attempting.
There is also another gotcha relating to the use of Backup & Restore. The Backup & Restore process was overhauled in FPBX 14 and above. This allows a Backup from one version FPBX 14 or higher to be Restored on a different version of FPBX 14 or higher. This new feature will not work with a Backup from FPBX 13 to a Restore on a higher version.
The answer is to do:
- Update your setups for Trunks and Extensions to use PJSIP.
- Do an in place update from FPBX 13 to FPBX 14.
- Then, take a Backup of your FPBX 14 machine to Restore on your new FPBX 16 machine.
- After the Restore onto the new machine, I experienced a series of script errors. Read them and acknowledge, the script took care of fixing each one. There were several reboots in the process. Apparently this was necessary to get some of the older setups in FPBX 14 up to snuff in FPBX 16.
There are several good threads about this process on the forum.
Always remember, don’t burn bridges. Good Backups. Leave the old server in place but off until you are satisfied that the new installation is sound and working.
Here is a resource post: FreePBX/Asterisk upgrade recommendations
Do be careful that the links to the wiki will likely not work since it has moved. Do a search on the referenced article on the new wiki.