The type of matriz is an integer pointer (array). In this case, when you have the operation matriz[i], the value you have is an integer. The problem is that you are trying to access the index [j] of that entire value.
You need to declare the parameter matriz as a array of arrays (or pointer pointer) to be able to access it via two indexes, as in the example below:
int contagemlinha(int ** matriz, int L, int C) {
    int i, j, soma = 0;
    for (i = 0; i < L; i++)
        for (j = 0; j < C; j++)
            soma += matrix[i][j];
    return soma;
}
Another way to store two-dimensional matrices is to store it in a simple array, with the elements of the first line followed by the elements of the second, and so on. For example, the matrix
1  2  3  4
5  6  7  8
9 10 11 12
Can be stored in the array
1  2  3  4  5  6  7  8  9 10 11 12
If that’s your case, then you just need to scroll through the matrix with an index:
int contagemlinha(int* matriz, int N)
{
    int i, soma = 0;
    for(i = 0; i < N; i++)
        soma += matriz[i];
    return soma;
}
							
							
						 
No need to increase
ialso?i++;belowsoma += ...– stderr