I have searched through the PayPal documentation, and I can't find a way to test a declined payment scenario using the REST API.
I saw this question on StackOverflow and it seems to indicate some test scenarios can be accomplished through the REST API, however, the answer is not immediately clear and my testing has not allowed me to produce a declined payment.
Here is what I've tried, with no success:
I've enabled Negative Testing in the Sandbox Account Details for the Business / Payee account.
I've run a number of transactions with different amounts (such as 105.34, 105.35, 105.39, among many others) as per these instructions, but all payments complete successfully.
Perhaps I'm missing something. Any advice would be much appreciated. Thank you!