USB Dongle install Entware on micro SD Card

[juanantonio]

Good afternoon everyone.

I have two Asus routers. My main router is a RT-AX86U, which is located in my main house.
The secondary one is a RT-AC86U, which is located at my town's house.
I've bought a ZTE MF833U1 USB 4G dongle, with the intention of giving internet access to my town's house, connecting it at USB port of RT-AC86U.
I have Wireguard Manager AddOn installed on both routers, installed on USB sticks through Entware.
The issue I have encountered is as follows:
I have connected the ZTE dongle to my RT-AX86U. The micro SIM card inserted into it is available through amtm to format it or install Wireguard (which is my goal, but on the RT-AC86U).
Surprisingly, when I want to format it on the RT-AC86U, amtm does not see the micro SIM card, so I cannot install Wireguard Manager AddOn on it, even though drive is recognized by the router (if I run 'fdisk -l' command, it is shown as /dev/sdb1).
The question is: is there I can do to have the micro SIM drive recognized by AMTM in the RT-AC86U as effectively it is in the RT-AX86U? The firmware on the RT-AX86U is Merlin 388.1 while in the RT-AC86U is Merlin 386.9.

Thanks in advance.