User-defined command and BLE GATT API not working

[rayyyy]

Hi,
I developped a firmware on STM32 in order to communication with my ESP32 through UART.
On ESP32 I only use the BLE module. Wifi is disabled.
STM32 sending AT commands in order to set all BLE parameters.
Through the BLE I'm able to update STM32 firmware, by sending new firmware to an external flash.

So for each packet of data received, the STM32 have to send the command AT+BLEGATTSSETATTR to update characteristic value followed by AT+BLEGATTSNTFY to notify client of the changed value.

This way of programming makes the file transfer very slow. I found that some user-defined AT commands can be added to the set of AT commands.
So the idea is to create an AT command that can accept command + data on the same frame and execute a characteristic value update and a notification update.

I made the cmd AT+TEST, but every time I use BLE GATT API the module reset
the screenshots show the code I used and the esp32 response when using AT+TEST command.

NB: Baudrate is 115200 but the delay is mostly affected by the main loop of the STM32 program.

Thank you for your help