When mapping a DID number to a VoIP line which is using a SIP protocol, please make sure to enter it together with a correct country code. For example:
The DID number is 8745441221 but it is a UK number, thus has to be preceded by an international access code for UK “44”.
Its mapping then looks as follows:
SIP/184.108.40.206/448745441221 AS OPPOSED TO SIP/220.127.116.11/8745441221.