Issue with json_scanf

main.c

#include <stdio.h>

#include "common/cs_dbg.h"
#include "common/json_utils.h"
#include "common/platform.h"
#include "fw/src/mgos_app.h"
#include "fw/src/mgos_rpc.h"

static void mangle_params(struct mg_rpc_request_info *ri, void *cb_arg,
                          struct mg_rpc_frame_info *fi,
                          struct mg_str args) {

  LOG(LL_DEBUG, ("args.p=%s, args.len=%d, ri->args_fmt=%s", args.p, args.len, ri->args_fmt));

  struct mbuf fb;
  struct json_out out = JSON_OUT_MBUF(&fb);

  mbuf_init(&fb, 50);

  int num = -1;
  bool fact1 = false, fact2 = false;
  json_scanf(args.p, args.len, ri->args_fmt, &num, &fact1, &fact2);

  if (num < 0) {
    mg_rpc_send_errorf(ri, 400, "Invalid num");
    ri = NULL;
    goto clean;
  }
  json_printf(&out, "{num: %d, fact1: %B, fact2: %B, or: %B, and: %B}",
    num + 1,
    fact1,
    fact2,
    fact1 || fact2,
    fact1 && fact2
  );

  mg_rpc_send_responsef(ri, "%.*s", fb.len, fb.buf);
  ri = NULL;

clean:
  mbuf_free(&fb);

  (void) cb_arg;
  (void) fi;
}

enum mgos_app_init_result mgos_app_init(void) {
  struct mg_rpc *c = mgos_rpc_get_global();
  mg_rpc_add_handler(c, "My.Test", "{num: %d, fact1:%B, fact2:%B}", mangle_params, NULL);
  return MGOS_APP_INIT_SUCCESS;
}