SFML Snake recreation in C++ - Fruit spawning on Snake's body

I know this is rookie code, but it's the first project I've made. I thought my logic was working, but sadly the fruit still manages to spawn on the snake's body.

Note: The sf::Vector2f 'movement' is what I'm setting the head's position to earlier in the code.

The std::vector<sf::RectangleShape> snake_body is a container that holds all of the snake's body tiles.

The random_location y coordinate has 1 being added to it because at the top of the screen is an extra row of tiles where a score counter is located, and the player cannot go there.

Everything works fine in my game except the spawning of the fruit is on the Snake's body. I know I can fix some things, but this specific problem I've been working on for hours with no success. Here's my function to spawn the fruit:

sf::Vector2f spawn_fruit(sf::Vector2f movement, sf::RectangleShape fruit, std::vector<sf::RectangleShape> snake_body) {

    sf::Vector2f random_location;
    std::srand(time(NULL));

    // flag set to true to loop to see if there is actually collision
    bool collision = true;

    while (collision) {
        // if there is no collision, it will stay false
        collision = false;
        // set spawn location based on time elapsed (cheap way to make random numbers)
        random_location.x = rand() % GRID_WIDTH;
        random_location.y = rand() % GRID_HEIGHT + 1;

        // make sure x and y isn't the same as the snake's current x and y
        if (random_location.x == movement.x && random_location.y == movement.y) collision = true;

        // make sure x and y isn't the same as snake body's current x and y
        for (int i = 0; i < snake_body.size(); i++) {
            if (snake_body[i].getPosition().x == random_location.x && snake_body[i].getPosition().y == random_location.y) {
                collision = true;
                break;
            }

        }
    }

    // return the vector
    return random_location;
}

Any help would be much appreciated. Thanks!