Find all pairs in an array that sum to a given number without using HashMap
Typo in method name as pointed out by @Stingy. Should be findAllPairs.
Accessing wrong array: You are reading values from input instead of your sorted copy numbers. This is probably a typo. E.g. int sum = input[low] + input[high]; should be int sum = numbers[low] + numbers[high];
Your for loop has an empty update statement, this isn't wrong per-se but a bit unusual. Consider an alternative using while instead:

int low = 0, high = numbers.length-1;
while (low &lt; high) {
    int sum = numbers[low] + numbers[high];
    //...
}

Insufficient test: As evidenced by its failure to catch the bug in 2. the test is too limited to be of much help. Consider checking more than one example (especially corner-cases like an empty input array) and checking against the expected output instead of just its size.