lte_send_atcmd_sync says inappropriate I/O for device

I am using NuttX 12.2.1 on an stm32 nucleo f103rb with a SIM7600G-H to try to use an AT command (via the LTE library).

This is how I am using the AT command:
int customhello_main(int argc, char *argv[])
{
char respbuff[15];
int x = **lte_send_atcmd_sync("AT\r", 3,
respbuff, 15,
15);**
printf("%s", respbuff);
printf("%d",x);

return 0;
}

In summary I am just sending an AT command hoping to get “OK”, but instead am getting the error code -25 (inappropriate i/o for device). I tried finding more info on this error but it is very general.

**How do I set up IO appropriately for AT commands and avoid these issues?**

More details:

- For configuration: I have GPIO debug features enabled. Under stm32 peripheral support, I have USART2 enabled for the SIM . Under I/O I have FILE stream enabled. Under networking, I have late driver init, udp, and tcp enabled. Under LTE I have deprecated API enabled.

- I have tried using USART1 instead of USART2, but I am getting the same error.

- Also, when running make, I am seeing this:

CC: chip/stm32_dumpgpio.c In file included from chip/stm32_dumpgpio.c:34:
chip/stm32_dumpgpio.c: In function 'stm32_dumpgpio':
chip/stm32_dumpgpio.c:110:9: warning: format '%x' expects argument of type 'unsigned int', but argument 4 has type 'uint32_t' {aka 'long unsigned int'} [-Wformat=]
110 | _info("GPIO%c pinset: %08x base: %08x -- %s\n",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
111 | g_portchar[port], pinset, base, msg);
| ~~~~~~
| |
| uint32_t {aka long unsigned int}
chip/stm32_dumpgpio.c:110:28: note: format string is defined here
110 | _info("GPIO%c pinset: %08x base: %08x -- %s\n",
| ~~~^
| |
| unsigned int
| %08lx