hi,Please help me about RB450G

I come from China, can not speak English, if rude, please forgive me.
This is the case:
I use RB450G Web Proxy in the 4G SD card, single-WAN can work, but can not work Multi-WAN.
Who can give me some tips, pictures or command.
Thank you!
QQ截图未命名1.jpg
QQ截图未命名.jpg

My setting
I wondered if I stated my thoughts accurately.
web proxy.jpg
nat2.jpg
nat.jpg