Help with Bandwidth Limiter and MultiWan set-up

Hi,

i need some help or explanation.
I'm using RT-N66U and latest MIPS version of firmware: 2019.3.220-beta.

My problem is whatever I try to do I can't enable wireless bandwidth limiter.

My connection is like this:
- two WANs

1st one:
- on USB port is connected Android from which I share mobile internet over USB tethering. This connection doesn't need limit

2nd one:
- direct internet PPPoE connection which is connected to the WAN port on the router from other router - connection is made...

Help with Bandwidth Limiter and MultiWan set-up