Route inbound 800's to SIP IVR

I am a new Asterisk/ FreePBX user and am stuck on a seemingly simple issue. I have toll free numbers routed from my SIP provider to the Asterisk. All I need to do is look at the toll free NPANXX and route it out to my SIP IVR . By manually editing extensions-additional.conf, I can do it with this line:
exten => 8661234567,3,Dial(sip/[email protected],60,m)

however any updates through FreePBX overwrite the manually edited file. So I tried to create an extension for my toll free number in FreePBX as follows:
Add Extension as Other (Custom) Device. Display Name = the toll free number, say 8661234567 and,
Device Options = sip/[email protected]

(The IP address and 866 # in the real config are obviously different )

The first call to each toll free works after a long pause, but the rest go to fast busy. In debug, I see only the first send an Invite to my IVR.

If I dial the 866# from an extension tied off of the PBX (an X-Lite Phone) the calls get routed properly every time.

Is there a step missing in my config? Do I need dial rules if I use the extension? Again, all I want to do is route certain calls to a SIP IVR based on dialed digits.

Thanks