SIP trace won't show the DTMF. Digits would normally probably be sent via RFC2833 packets, which would show in a packet trace of the RTP stream.
In your case you're running start_dtmf and start_dtmf_generate - are you sure you want those? They are for receiving and sending DTMF as in-band DTMF tones instead of as SIP INFO / RTP RFC2833 packets. They're not a good idea unless you actually require them since they increase the CPU load for the call and can result in duplicated digits if you're sending DTMF both inband and out-of-band.
For debugging purposes DTMF packets sent via start_dtmf_generate cannot be seen in packet traces, unless you actually decode and listen to the RTP stream they're sent in.
If the device you're sending to isn't hearing the digits it probably means start_dtmf_generate is sending them inband and the device is only listening for DTMF out-of-band.