Equipment TP-MR3020 v3. Huawei e3531 modem is connected.
Installed firmware
DISTRIB_ID='OpenWrt'
DISTRIB_RELEASE='SNAPSHOT'
DISTRIB_REVISION='r8629-f98fde2db4'
DISTRIB_TARGET='ramips/mt76x8'
DISTRIB_ARCH='mipsel_24kc'
DISTRIB_DESCRIPTION='OpenWrt SNAPSHOT r8629-f98fde2db4'
DISTRIB_TAINTS=''
Installed a modem according to the instructions https://openwrt.org/docs/guide-user/network/wan/wwan/3gdongle.
After connect web interface show error
Device is determined by /dev/ttyUSB0, /dev/ttyUSB1