The agency didn't detect the error because it didn't test the product. It took us a few days to find the error, and then we rectified the situation.
That doesn't erase the harm done to the 10,000 Canadians affected, which is completely unacceptable. However, given that 30 million travellers have used the app, those affected by the error are an exception.
This doesn't preclude the fact that it was completely unacceptable that the agency did not find this error before the app was used by the public.