Make sure you have correctly chosen the Arduino DUE and that your App, libraries, etc. are all updated.
And as per the FAQ at end of the documents…
- How many Virtual Pins I can use?
It depends mostly on your hardware. Low-end hardware may use up to 32 Virtual Pins. More powerful (like ESP8266) can use up to 128 but it requires also BLYNK_USE_128_VPINS property in your sketch. Example.
// Uncomment to force-enable 128 virtual pins