If the Serial.println() does not accept the uint64_t, then try the sprintf().
The Serial.println() is from the Arduino code. The sprintf() is from the libraries that belong to the compiler.
The sprintf() is not straightforward for 64 bit. You might have to use "%I64u" or "%llu" or even "%"PRIu64", but I don't understand what that last one is. You could start with the most common "%lld".