I will help if I can.
Please show me the output of pjsip show endpoints. Please be sure to sanitize any sensitive information.
On the snom, are you using a blf field or XML-Definition. Also please show me what core show hints prints out. In the asterisk cli are there any warnings when the snom registers for blf?
I am assuming you are using asterisk without freepbx but please correct me if my assumption is incorrect.
Does the snom phone you are using have the ability to support XML-Definitions? If you are unsure I can look it up.