app_uart_get more than 1 byte

Question

Hi, 
 I'm using app_uart for communication between different mcu. I can send more than 1 byte like "0x3917015623" through changing tx_buffer[0] to tx_buffer[5] . Unfortunately i couldn't recieve the slave devicess message " 0x2917013607 ". I can only get the first byte " 0x07 ". My configuration are the same as uart example. How can i recieve all the message ?. I tried to use serial library but i couldn't initialize. (It gave ERROR 6 NRF_ERROR_NOT_SUPPORTED ). 
 Slave device is sending me a message every second. And i'm calling app_uart_get function every 500 miliseconds. 
 
 Here is my uart init; 
 void uart_error_handle(app_uart_evt_t * p_event)
{
 if (p_event->evt_type == APP_UART_COMMUNICATION_ERROR)
 {
 APP_ERROR_HANDLER(p_event->data.error_communication);
 }
 else if (p_event->evt_type == APP_UART_FIFO_ERROR)
 {
 APP_ERROR_HANDLER(p_event->data.error_code);
 } 
}

void uart_init(void)
{
 uint32_t err_code;
 const app_uart_comm_params_t comm_params =
 {
 RX_PIN_NUMBER,
 TX_PIN_NUMBER,
 RTS_PIN_NUMBER,
 CTS_PIN_NUMBER,
 UART_HWFC,
 false,
 #if defined (UART_PRESENT)
 NRF_UART_BAUDRATE_115200
 #else
 NRF_UARTE_BAUDRATE_9600
 #endif
 };
// const app_uart_buffers_t m_buffers =
// {
// &rx_buffer_s,
// sizeof(rx_buffer_s),
// &tx_buffer_s,
// sizeof(tx_buffer_s)
// }
 APP_UART_FIFO_INIT(&comm_params,
 UART_RX_BUF_SIZE,
 UART_TX_BUF_SIZE,
 uart_error_handle,
 APP_IRQ_PRIORITY_LOWEST,
 err_code);

 APP_ERROR_CHECK(err_code);
// err_code = app_uart_init(&comm_params, &m_buffers, uart_error_handle, APP_IRQ_PRIORITY_LOW);
// APP_ERROR_CHECK(err_code);
 
} 
 
 Regards,