Obersable_server Unrecheable with Copper (firefox) On Raspberry Pi 3 B

Hi,

I'm trying to send CoAP messages from an Raspberry Pi3 B to an nRF52 DK with Obersve_server  on it.

What i've done :

I'ive edited radvd.conf like this :

then i've created a connexion.sh file :

Then : i've added the 2001:db8::1/64 prefix to bt0 interface with

ifconfig bt0 add 2001:db8::1/64

and i've checked the bt0 interface :

A inet6 2001:db8::b827:ebff:fe9b:9a23 should be present ? so ive added it manually

ifconfig bt0 add 2001:db8::b827:ebff:fe9b:9a23/64

Then i've ping the device with the local address :

and the global adress :

FInally i've tried to send a message with Copper (Firefox) with the following adress "coap://[2001:db8::b827:ebff:fe9b:9a23]/:5683"  but i've always the same message : "Warning : Message xxxx timed out"

I don't know what i've done wrong and I hope you can help me...

Sorry if my English isn't correct, it's not my main language.