nRF9160 SLM-specific AT commands (ie AT#XHTTPCCON?) via firmware functions?

Question

I am using an nrf9160DK with modem firmware v1.3.2.

I want to be able to send the "AT#" type of SLM-specific AT commands to the modem (and read the response back) via firmware on the nRF9160.

In the lte_serial_mode example, I use the nrf_modem_at_cmd() function. Using the AT commands (AT+ and AT%) does not generate any errors while with the "SLM specific AT commands" (AT#) it generates an error.

CODE:

err = nrf_modem_at_cmd(buf_rx, 500, "AT%%XTEMPHIGHLVL?");

	for (int i = 0; i < 20; i++)
	{
		printk("%c",buf_rx[i]);
		buf_rx[i] = 0;
	}
	printk("%c\n",buf_rx[20]);
	buf_rx[20] = 0;

	if (err == (0)) {
		/* OK, success */
		printk("OK, success\n");
			
	}
	else if (err < 0) {
		/* Failed to send command, err is an nrf_errno */
		printk("error < 0\n");
	}
	else if (err > 0) {
		/* Command was sent, but response is not "OK" */
		gpio_pin_toggle(ledINT, PINLEDINT);
		printk("error > 0\n");
		switch(nrf_modem_at_err_type(err)) {
		case NRF_MODEM_AT_ERROR:
			/* Modem returned "ERROR" */
			printk("error\n");
			break;
		case NRF_MODEM_AT_CME_ERROR:
			/* Modem returned "+CME ERROR" */
			printk("cme error: %d\n", nrf_modem_at_err(err));
			break;
		case NRF_MODEM_AT_CMS_ERROR:
			/* Modem returned "+CMS ERROR" */
			printk("cms error: %d\n", nrf_modem_at_err(err));
			break;
		}
	}

	err = nrf_modem_at_cmd(buf_rx, 500, "AT#XHTTPCCON?");

	for (int i = 0; i < 20; i++)
	{
		printk("%c",buf_rx[i]);
		buf_rx[i] = 0;
	}
	printk("%c\n",buf_rx[20]);
	buf_rx[20] = 0;

	if (err == (0)) {
		/* OK, success */
		printk("OK, success\n");
	}
	else if (err < 0) {
		/* Failed to send command, err is an nrf_errno */
		printk("error < 0\n");
	}
	else if (err > 0) {
    	/* Command was sent, but response is not "OK" */
    	printk("error > 0\n");
    	switch(nrf_modem_at_err_type(err)) {
    	case NRF_MODEM_AT_ERROR:
    		/* Modem returned "ERROR" */
    		printk("error\n");
    		break;
    	case NRF_MODEM_AT_CME_ERROR:
    		/* Modem returned "+CME ERROR" */
    		printk("cme error: %d\n", nrf_modem_at_err(err));
    		break;
    	case NRF_MODEM_AT_CMS_ERROR:
    		/* Modem returned "+CMS ERROR" */
    		printk("cms error: %d\n", nrf_modem_at_err(err));
    		break;
    	}
	}

LTE LINK MONITOR RESPONCE

If the "SLM-specific AT commands" are sent from the terminal of the nRF Connect LTE Link Monitor tool, they work correctly.

Could someone help me?

Thanks