There are 3 types of DTMF:

1. SIP INFO – sending of SIP message.
2. RFC2833 – sending of RTP packets sequence.
3. Inband – tone generation and sending the tone in RTP packets.

WCS3 supports modes 1 and 2.
RFC2833 – by default.

You need setup DTMF which is supported by your PBX.
If the PBX supports inband DTMF only, such DTMF will not work with WCS.