Wiaomi wifi 3g openwrt

Hello
I just received my router and I tried to install openwrt but it did not work I'm in firmware 2.28 .... when I try to put an older firmware (I'm trying 4) it puts me echec
how can I do ?

A post was merged into an existing topic: Xiaomi Wifi Router 3G - 18.06.X / feedback and help