We are working everyday on improving Advanced Caller ID for iOS Here are some known limitations:
Advanced Caller ID is not active for Truecaller app bellow version 11.36
Advanced Caller ID only works for US and Canada
Advanced Caller ID only works with carrier supporting Conditional Call Forwarding
Advanced Caller ID is by default active for both known and unknown contact
Advanced Caller ID prevents any caller to reach your voicemail
We are actively working on solving all these limitations.