Twilio cannot understand parts of your SIP URI. This may be due to invalid characters appearing in the user, params, or headers portion. While Twilio may still attempt to complete your call, the parts of the URI that are invalid will be ignored.
The format for a valid SIP URI is defined in RFC 3261.
0A1B2C3D;encoding=hex
, you must encode this into the URI as User-to-User=0A1B2C3D%3Bencoding%3Dhex
.