long write can not be implemented

[zkt-1400]

I want to implement a long write.
The environment in use is below.
· SDK15
· Nrf 52
· Nrf 52832_xxaa
· S132_nrf52_6.0.0_softdevice.hex

My start is "nRF5_SDK_15.0.0_a53641a \ examples \ ble_peripheral \ ble_app_uart".
I am adding my service to this. I referred to the following.
· github.com/.../custom_ble_service_example

I would like to implement a long write of maximum size 512 bytes for my service.
infocenter.nordicsemi.com/index.jsp

The current situation is below.

· Added to main.c

static uint8_t queued_write_buffer [1024]; / ​​** <LongWriteBuf
ble_user_mem_block_t mem_block; / ** <User Memory Block. * /

· Main.c - added to ble_evt_handler ()

    case BLE_EVT_USER_MEM_REQUEST:
        NRF_LOG_INFO ("BLE_EVT_USER_MEM_REQUEST");
        mem_block.len = sizeof (queued_write_buffer);
        mem_block.p_mem = & queued_write_buffer [0];
        err_code = sd_ble_user_mem_reply (m_conn_handle, & mem_block);
        APP_ERROR_CHECK (err_code);
        break;

    case BLE_EVT_USER_MEM_RELEASE:
        NRF_LOG_INFO ("BLE_EVT_USER_MEM_RELEASE");
        break;

    case BLE_GATTS_EVT_WRITE:
        NRF_LOG_INFO ("BLE_GATTS_EVT_WRITE");
        // Long write processing
        break;

problem:
The result of sd_ble_user_mem_reply () is as follows.
NRF_ERROR_INVALID_STATE (NRF_ERROR_BASE_NUM + 8)

Also, is nrf_ble_qwr_on_ble_evt () in nrf_ble_qwr.c unrelated to long writing?
I think the composition is similar.

Please give me some advice. Thank you.

[zkt-1400]

I solved this problem by using nrf_ble_qwr.c.

But I got a new question.

When writing less than 20 bytes, the length can be confirmed below.

· p_evt_write-> len

How do you check the length when it is longwrite?