For US demo merchant accounts
There are a number of ways to generate unsuccessful transactions from a demo account.
Simulate unapproved Bank Responses
You can use the dollar amounts between 5000.00 - 5999.00 to trigger a variety of Bank Responses, where the desired response code is added to 5000.
Simulate unsuccessful Ecommerce Responses
You can use the penny amounts to trigger a variety of eCommerce Responses, where the desired response code is added to 5000.00.
For example, to simulate a transaction that encountered the "Unable to Send Trans" error (code 42) during processing, use 5000.42 as the transaction amount.
Note: If both the dollar and penny amounts would trigger a simulated code (for example, 5200.42), the penny amount trigger will take precedence.