OP solved the task, closing

You are thinking as of [row][column] and the solution is [column][row]

For this kata, coordinates in the maze are 0-based. First coordinate is horizontal (x), increasing left to right, and the second one is vertical (y) increasing from top to bottom.
Such coordinate system is somewhat "customary" and I believe that's why it's not explained in details, but I've seen remarks in the comments that it's not sufficiently clarified in the description.

I am still confused, here is how i look to this:

Example 1:
     1 ##############      1 ############## 
     2 #        \   #      2 +--------\   # (2, 0)? or (1,0) if starts with 0
     3 *   \        #  =>  3 *---\    |   #
     4 #            #      4 #   |    |   #
     5 #   \    /   #      5 #   \----/   #
     6 ##############      6 ##############
       12345678901234 = 14 
Example 2:
      1###*###      ###*### 
      2#/ /  #      #/-/  # 
      3#     #  =>  #|    #
      4#     #      #|    #
      5#\    #      #\----+ (5,7) or (4,6) if starts with 0
      6#######      #######
       1234567 = 7

Am I misunderstanding something here?

You have to be careful when reading the mazes, because in C++, backslashes are escaped what makes them tricky to read. Without escaped characters, mazes look like this:

Example 1:
      ##############       ##############
      #        \   #       +--------\   #
      *   \        #  =>   *---\    |   #
      #            #       #   |    |   #
      #   \    /   #       #   \----/   #
      ##############       ##############

Example 2:
      ###*###      ###*### 
      #/ /  #      #/-/  #
      #     #  =>  #|    #
      #     #      #|    #
      #\    #      #\----+
      #######      #######

I marked places where beam exits the maze with +, and they are located at (0,1) for the first maze, and (6,4) for the second maze.

How first answer of is equal to (0,1)? Isn't it (1,0)?

Describe(exit_from_maze_tests) {
  It (passes_example) {
    Board m {
      "##############",
      "#        \\   #",
      "*   \\        #",
      "#            #",
      "#   \\    /   #",
      "##############"
    };
    Assert::That(exit_from_maze(m), Equals(Result({0, 1}, 22)));
  }

The same second example: it should end on (5, 7)! how it is (6,4)?

 It (passes_second_tests) {
    Board m {
      "###*###",
      "#/ /  #",
      "#     #",
      "#     #",
      "#\\    #",
      "#######",
    };
    Assert::That(exit_from_maze(m), Equals(Result({6, 4}, 10)));
  }
};

I am totally confused, with how answers have gotten? Can you explain me, please!

To start with, remove the line

len -= 3;

Also, I recommend you convert the C-style string to a C++ string.

string in_string(in); 

This might help refactor the code and simplify it further.

Read this, try Github channels if you're in a hurry.

If there is no help, where i can find some hints?

Checked the code, answers is correct, however output says:

Expected: equal to another value

Actual: some value

Havent' seen that type of question in the comments bellow.

Thank you very much for quick and comprehensive reply. I do appreciate that!

Thanks for sharing. It's interesting to me cuz I never had that error.

By some quick debugging I found the problem: your for loop initializes unsigned int until it goes negative. But here's the problem with unsigned - it doesn't go negative :P Once you try to do 0 - 1, it results in 4294967295, which is still >= 0, and when you try to access a character at that index, you get this error.

I hope that's helpful. There are still some logical errors in your code, but this should get you started :>