Misc. Dialplan Tools flush dtmf
From FreeSWITCH Wiki
Flushes DTMFs received on a channel. Useful in cases where callers may have entered extra digits in one dialog and you want to flush them out before sending them into another dialog. (See play_and_get_digits)
If you have issues with mysterious DTMFs being entered in your dialogs then try adding flush_dtmf before the dialog and see if that helps.