You need to manually configure the chan_dahdi.conf, as mentioned above:
[channels]
;Configuracao para MFC/R2
signalling=mfcr2
mfcr2_variant=br
mfcr2_get_ani_first=no
mfcr2_max_ani=20
mfcr2_max_dnis=4
mfcr2_category=national_subscriber
mfcr2_logdir=span1
mfcr2_call_files=yes
mfcr2_logging=all
mfcr2_mfback_timeout=-1
mfcr2_metering_pulse_timeout=-1
mfcr2_allow_collect_calls=no
mfcr2_double_answer=yes
mfcr2_immediate_accept=no
mfcr2_forced_release=no
mfcr2_charge_calls=yes
mfcr2_advanced_protocol_file=/etc/r2proto.conf
language=pt_BR
echocancel=yes
echocancelwhenbridged=no
context=entrada-e1
callgroup=0
pickupgroup=0
group=1
channel =>1-15,17-31
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