You might get the following error:

Unable to initialize.
Make sure the daemon is running.
Error: Process /usr/lib/sflphone/sflphoned exited with status 1

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This mean the last process didn't shut down properly and let a PID file lie around. You can delete it with

rm ~/.cache/sflphone/sfl.pid

(If you've shut sflphone down some seconds ago, you just have to wait 10 seconds and don't have to remove the pid file manually)