@jkandasa Thank you for your help: I summarize what you asked me to do and which works now:
The (minimum) equipment to test FOTA: I have a ATMega 328p BareBones (8MHz internal) + led attached to PB1 (pin15)+ SPI Flash memory + 3.3v regulator + RFM69HCW.

Install ArduinoISP program to ProMini (Programmer) Connect MySensors board on ProMini (ArduinoISP) via ISP header Select, Programmer="Arduino as ISP", Board:"Sensbender Micro", Processor:"Atmega 328 8Mhz" Now click on "Burn Bootloader". bootloader will be loaded on MySensors board Remove ISP header and remove ProMini from your computer Connect MySensors board to USB via FTDI connector Upload MySensors sketch(OTA should be enabled on the sketch) to MySensors board Now the MySensors node will appear in MyController server. Modify the MySensors sketch and upload it to MyController Now trigger "Firmware upload" from MyController server page.

This is the first sketch to upload one time with the USB to FTDI connector :

//pr1: minimal sketch for fota with blink led #define blinkTime 200 #define SKETCH_NAME "SensBender Led 200 -70" //25 caracteres max #define SKETCH_VERSION "pr1" //===== RFM config ===== // Enable and select radio type attached #define MY_RADIO_RFM69 //#define MY_DEBUG_VERBOSE_RFM69 //#define MY_DEBUG_VERBOSE_RFM69_REGISTERS #define MY_RFM69_NEW_DRIVER //#define MY_RFM69_ATC_MODE_DISABLED #define MY_RFM69_ATC_TARGET_RSSI_DBM (-70) // target RSSI -70dBm//BUG //#define MY_RFM69_MAX_POWER_LEVEL_DBM (20) // max. TX power 10dBm = 10mW//MARCHE #define MY_RFM69_FREQUENCY (RFM69_868MHZ) #define MY_IS_RFM69HW //with H(CW) //#define MY_RFM69HW (true) //#define MY_RFM69_NETWORKID (100) //#define MY_RFM69_BITRATE_MSB (RFM69_BITRATEMSB_1200) //#define MY_RFM69_BITRATE_LSB (RFM69_BITRATELSB_1200) // Enable repeater functionality for this node //#define MY_REPEATER_FEATURE #define MY_DEBUG //===== LED ===== #define LED_BUILTIN 9 //pb1 pin15 //===== This Node ID ===== #define MY_NODE_ID 0x02 //===== Enable OTA feature ===== #define MY_OTA_FIRMWARE_FEATURE #define MY_OTA_FLASH_SS (8) //pb0 pin14 #define MY_OTA_FLASH_JDECID 0x00 //0x00 if you don't know #include <MySensors.h> //=================================== //= SETUP = //=================================== void setup() {//pas besoin de Serial.begin(115200) pinMode(LED_BUILTIN, OUTPUT); Serial.print("Start "); Serial.print(SKETCH_NAME); Serial.print(" "); Serial.println(SKETCH_VERSION); }//FIN du SETUP //========================================== //= PRESENTATION = //========================================== void presentation() { // Send the sketch version information to the gateway and controller sendSketchInfo(SKETCH_NAME, SKETCH_VERSION); } // FIN de PRESENTATION //=================================== //= LOOP = //=================================== void loop() { digitalWrite(LED_BUILTIN, HIGH); Serial.print("LED ON "); wait(blinkTime); digitalWrite(LED_BUILTIN, LOW); Serial.println("LED OFF "); wait(blinkTime); }// FIN de LOOP

Change blinkTime time and compil the sketch , then upload firmware .hex with MYCONTROLLER.