I found a workaround, rather than Dialing the multicast address, I make a system call to ffmpeg
same => n,System(/usr/bin/ffmpeg -re -i /var/lib/asterisk/sounds/en/custom/dingdong.wav -filter_complex 'aresample=8000,asetnsamples=n=160' -ac 1 -vn -f rtp rtp://239.255.0.1:4001)