Card Declined: Card Number 4000000000000002
Incorrect Number: Card Number 4242424242424241
Disputed Transaction: Card Number 4000000000000259
Invalid Expiration Date: Try any invalid sequence of numbers, such as 55
Invalid Security Code: Any 2 digits
You should use the responses on both to make sure that notifications are going to the correct departments so you can address them accordingly or adjust your sales process.