How does the license work?

Hi all,

I had an old FreePBX 3 working behind a firewall with no access to any other devices except 2 phones and the SIP trunk. (So no big issue from the security standpoint, even without updating it)

It stopped working suddenly, for an hardware failure, and when I tried reinstall and restore the old configuration backup it seemed to work for few minutes, but then it asked for a license to use the outbound SIP trunk. (I tried to reinstall several version: from v4 to the last v16 and they all had the same problem)

Do I have to pay or buy anything to keep it working?
Or do I just need to register for the free license?

I don’t understand what is free to use or how to proceed… Can anyone help me understand what to do please?

There is no paid license required to make trunking work.