Not receiving CoAP messages on Border Router

[Mary]

nRF52840
NCS 3.0.1
MCUBOOT

OTBR on Raspberry Pi 4

I am running the OTBR on a Raspberry Pi 4 with the RCP on a dongle.  I am running the coap_client on a nRF52840DK.  I have written a simple coap server for the Raspberry Pi, but it is not seeing any messages.

coap server code

#include <coap3/coap.h>
#include <stdio.h>
#include <string.h>

int getCnt = 0;

void hnd_provisioning_get(coap_resource_t *resource,
                     coap_session_t *session,
                     const coap_pdu_t *request,
                     const coap_string_t *query,
                     coap_pdu_t *response)
{
	getCnt++;

	time_t now;
	now = time(NULL);
	
	printf("Provisioning GET received %d times.\n", getCnt);

	unsigned char buf[] = "Provisioning response";

	coap_pdu_set_code(response, COAP_RESPONSE_CODE_CONTENT);
	coap_add_data(response, strlen((char *)buf), buf);

} //end: hnd_provisioning_get()

int main(void)
{
	coap_context_t *ctx=NULL;
	coap_resource_t *resource=NULL;
	coap_endpoint_t *endpoint=NULL;
	struct coap_address_t addr;

	// Initialize libcoap
	coap_startup();

	// Set up the server address (UDP, port 5683)
	// Set up for IPv6 wildcard address
 	coap_address_init(&addr);
   	addr.addr.sin6.sin6_family = AF_INET6;
    	addr.addr.sin6.sin6_addr = in6addr_any; 		// Listen on any IPv6 address
    	addr.addr.sin6.sin6_port = htons(COAP_DEFAULT_PORT); 	// Default CoAP port (5683)
    	addr.size = sizeof(addr.addr.sin6);

	// Create CoAP context
	ctx = coap_new_context(NULL);
	if (!ctx)
	{
		printf("Cannot create CoAP context\n");
		return -1;
	}

	
	// Create UDP endpoint
	endpoint = coap_new_endpoint(ctx, &addr, COAP_PROTO_UDP);
	if (!endpoint)
	{
		printf("Cannot create endpoint\n");
		coap_free_context(ctx);
		coap_cleanup();
		return -1;
	}

	// Create resources
	resource = coap_resource_init(coap_make_str_const("provisioning"),0);
	if (!resource)
	{
		printf("Cannot create resource: provisioning\n");
		coap_free_context(ctx);
		coap_cleanup();
		return -1;
	}

	// Register GET handlers
	coap_register_handler(resource,COAP_REQUEST_GET, hnd_provisioning_get);

	// Add resource to context
	coap_add_resource(ctx, resource);
	
	printf("CoAP server running on port %d...\n", COAP_DEFAULT_PORT);
	
	// Main loop to process CoAP packets
	while(1)
	{
		//coap_io_process(ctx, COAP_IO_NO_WAIT);
		coap_io_process(ctx, COAP_IO_WAIT);		// MSEC
printf("\rGetCnt: %d", getCnt);
	} // endwhile: 1

	// Cleanup
	coap_free_context(ctx);
	coap_cleanup();

	return 0;
} //end: main()

When I run the coap_server and then restart the coap_client, I can see the "provisionng" messages on Wireshark, but there is no response from the coap server.

The Raspberry Pi shows:

c@raspberrypi4:~/coap_server $ ./coap_server
CoAP server running on port 5683...

If I run netcat, it seems to receive the UDP message from the coap_client:

:~/coap_server $ netcat -lu :: 5683
H+}▒u▒=T▒▒provisioning▒▒▒6▒R▒▒^C

What's wrong with my setup?

Mary