BLF configuration in the dialplan

Hi all,
How to manage the BLF state in the extension_custom.conf.I have a dialplan such as

exten => 900,n,Set(DEVICE_STATE(Custom:DEVDND)=RINGING)
exten => 900,hint,Custom:DEVDND
exten => 900,Macro(hangupcall,)

in this state,the BLF is always blinking,

How to stop BLF blinking?

Help me!

You would have to change the device state somewhere to be not in use or a different state. You appear to be using FreePBX, so where would be the best spot - I do not know.

Thank Jcolp for your reply.