Cannot install libmraa via radxa apt

Hi,

I tried to install mraa on Rock Pi S on Ubuntu 20.04 but Radxa Apt cannot install it. Info as following:

lsb_release -a

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.3 LTS
Release: 20.04
Codename: focal

cat /etc/apt/sources.list.d/apt-radxa-com.list

deb http://apt.radxa.com/focal-stable/ focal main
deb http://apt.radxa.com/focal-testing/ focal main

sudo apt install libmraa

Reading package lists… Done
Building dependency tree
Reading state information… Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libmraa : Depends: libjson-c3 but it is not installable
E: Unable to correct problems, you have held broken packages.

apt search libjson-c3

Sorting… Done
Full Text Search… Done

I also tried to compile it using this link:https://github.com/brian541/mraa/blob/master/docs/building.md
But after compiling I got:

mraa-gpio list

No Pins

Thank you very much.

I found one github repo that works:this