While this might sound mean, I don’t intend it to be.
This is a pure Asterisk problem - while there might be people here that might be able to help you, I think you’d be more likely to find the resources you need on the Asterisk.org forums. I’m certainly not suggesting that you need to stop posting - I’m just saying that the folks at Asterisk.org might be a better resource since they are one layer closer to the system then we are.
Once you get the details worked out, I’m sure we’d all love to hear about how you did it, but this doesn’t really have any relation to FreePBX. At least, not until you get it working and put in an Issues ticket to add it as an enhancement.
Actually is a Chan_Dongle issue not asterisk not freepbx.
The error is telling you that Chan_Dongle is already loaded in your asterisk, and the secod is telling you that the interface on the linux system doesn’t exist. So first of all check which device is using linux to configure the USB-CDC by running:
Or unplug the usb modem run the command
attach again the usb and look in the log which tty is assigned to it.
Then go and edit the /etc/asterisk/dongle.conf file accordingly. Save changes, go back to the cli, unload the module, load the module and try again.