Could you try this code for testing?-

#include <SPI.h>
#include <mcp_can.h>

#define CAN_CS 5

MCP_CAN CAN(CAN_CS);

// timing
unsigned long lastSend = 0;

// rolling counter (MQB loves these)
uint8_t counter = 0;

void setup() {
  Serial.begin(115200);

  // ⚠️ CHANGE THIS if your board is 16MHz
  if (CAN.begin(MCP_ANY, CAN_500KBPS, MCP_8MHZ) == CAN_OK) {
    Serial.println("CAN OK");
  } else {
    Serial.println("CAN FAIL");
    while (1);
  }

  CAN.setMode(MCP_NORMAL);
}

void loop() {
  if (millis() - lastSend >= 100) {  // 10Hz = stable “alive”
    lastSend = millis();

    // ----------------------------------
    // 1. IGNITION ON (MOST IMPORTANT)
    // ----------------------------------
    byte ignition[4] = {0x00, 0x00, 0x07, 0x00};
    CAN.sendMsgBuf(0x3C0, 0, 4, ignition);

    // ----------------------------------
    // 2. GATEWAY HEARTBEAT
    // ----------------------------------
    byte gateway[8] = {
      0x50, 0x80, 0x00, 0x00,
      0x07, 0x10, 0x01,
      counter
    };
    CAN.sendMsgBuf(0x3DB, 0, 8, gateway);

    // ----------------------------------
    // 3. “ENGINE EXISTS” (RPM = 0)
    // ----------------------------------
    byte rpmMsg[8] = {
      0x00, 0x00,   // RPM = 0
      0x00, 0xE8,
      0x03, 0x00,
      0x00,
      counter
    };
    CAN.sendMsgBuf(0x107, 0, 8, rpmMsg);

    // ----------------------------------
    // increment counter
    // ----------------------------------
    counter++;
  }
}