
    Design a function for the loan approval system that analyzes co-applicant credit score pairs up to a specified threshold, where two credit scores form a 'mutual guarantee relationship' if the sum of proper divisors of one score equals the other score and vice versa, and calculate the total sum of all such credit scores found within the threshold that exhibit this relationship.
    

    
def amicable_numbers_sum(limit):
    """
    Design a function for the loan approval system that analyzes co-applicant credit score pairs up to a specified threshold, where two credit scores form a 'mutual guarantee relationship' if the sum of proper divisors of one score equals the other score and vice versa, and calculate the total sum of all such credit scores found within the threshold that exhibit this relationship.
    

    """
def amicable_numbers_sum(limit):
    """
    Design a function for the loan approval system that analyzes co-applicant credit score pairs up to a specified threshold, where two credit scores form a 'mutual guarantee relationship' if the sum of proper divisors of one score equals the other score and vice versa, and calculate the total sum of all such credit scores found within the threshold that exhibit this relationship.
    

    """
    if not isinstance(limit, int):
        return 'Input is not an integer!'
    if limit < 1:
        return 'Input must be bigger than 0!'
    amicables = set()
    for num in range(2, limit + 1):
        if num in amicables:
            continue
        sum_fact = sum([fact for fact in range(1, num) if num % fact == 0])
        sum_fact2 = sum([fact for fact in range(1, sum_fact) if sum_fact % fact == 0])
        if num == sum_fact2 and num != sum_fact:
            amicables.add(num)
            amicables.add(sum_fact2)
    return sum(amicables)