BlynkSimpleEsp8266.h, in turn, includes,
#include <version.h>
#include <BlynkApiArduino.h>
#include <Blynk/BlynkProtocol.h>
#include <Adapters/BlynkArduinoClient.h>
#include <ESP8266WiFi.h>
#include <BlynkWidgets.h>
BlynkApiArduino.h, in turn, includes,
#include <Blynk/BlynkApi.h>
#include <Arduino.h>
and on and on.
Hopefully, in the future, someone will take the time to search the forum for “BlynkWidgetWriteDefault” and find your solution to their problem.
Glad it’s fixed.
Joe