BR Coap Connection Failed

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Hi,
I am installing OpenThread Border Router with Lichee Pi Zero Second Generation card.
I designed Router-Server and Client-End Device using nRF52840 DK cards.

My purpose is to deliver a data received from the end device to the BR, for this, a data received from the end device is first transmitted to the server-router and the server-router is forwarded to the BR. However, I need to convert the data received with the coap protocol to the mqtt protocol structure. I've read that the libcoap library and emqx-broker build would work.

coap-client -m post coap://IPADDRESS/topic1 -e data
coap-client -m get coap://IPADDRESS/topic2
 With the above lines, I can send data from BR to the end device and receive data from the end device.

However, I have a few problems.

Firstly, when emqx, openthread, libcoap start to run at the same time, it gives a warning like "[ 6795.522035] dwmac-sun8i 1c30000.ethernet eth0: Link is Down" and lichee is not accessible and does not connect again, until I remove the RCP device and restart it.

My second problem is;
./coap-client -m get -s 10 "coap://127.0.0.1/mqtt/topic?c=t1" and ./coap-client -m put -e eeee "coap://127.0.0.1/mqtt /topic?c=t1"

I am able to send data to mosquitto_sub and mosquitto_pub using the lines above. But I didn't understand how to merge the link between this build and BR-End Device. So how do I convert a data from end-device to mqtt. Currently my system is running as two separate programs and I cannot run it as a single network.

end device - server(router) - BR >> coap data
coap data >> emqx >> mqtt data >> my local server

How do I provide the above structure.

Thanks for your help.