How to simulate a VOID error?

I'm trying to code to handle errors on voids, but I can't simulate a void error by using a certain amount - 5000.07 (as documented here https://support.payeezy.com/hc/en-us/articles/204504175-How-to-generate-unsuccessful-transactions-during-testing-) because the amount doesn't match the inital purchase's amount. I can't use that amount on the initial purchase, as it will just error on the purchase and not generate the trans. codes for doing the void.... how can I get around this?