If you receive a long, and max value for long is of course 2147483647, then how would it be possible that you receive 6922181194580306956 as input?

Hint: cout << sizeof(long);.

This kata is a duplicate of other kata (for example, this one: https://www.codewars.com/kata/5254ca2719453dcc0b00027d) and most probably will not leave beta.

It is. The function that's being tested is (as provided in the initial code) this one:

bool valid_braces(std::string braces);

Your code doesn't contain something like this, therefore the error message.

You are wrong. We don't know what you are printing, but the kata is fine. Please stop spamming non senses and read this: https://docs.codewars.com/training/troubleshooting/