Pulse Dialing Failing

I have a Grandstream GS-HT701 and have set it to allow for pulse dialing, so I can connect an old rotary phone. When I start dialing the server (perhaps it is the ATA, really?) seems to be listening, but once I stop dialing and the number is sent to the server, I get a busy tone. I am running FreePBX over Asterisk and was hoping someone could help me configure things (either natively in Asterisk, or if I can do it via FreePBX, even better) to work correctly. I have looked around but haven’t found much about pulse dialing online! Thanks in advance!