When using Asterisk, you might see warning messages in the logfile or on the CLI "Unknown RTP codec 95 error".
You can safely ignore these messages, they are the result of Zoiper sending a fake small packet with rtp codec id 95 for the purpose of opening a NAT binding in case there is a NAT between Zoiper and the server.
This happens immediately after the call is answered, early media starts, or unhold session refresh (if SDP changes).
This should not cause any issues and it there only to speed up the process of the audio flowing in both directions.