If we wish to simulate a transaction flagged for retry how should we test?

Using card number 999202 will result in a declined transaction and set the retry flag to "1" for interfaces that support it.

What other tests can I perform in addition to the ones I have tried?

You could try the following card numbers to simulate other common declines:

999236 - ReCo 05

999269 - ReCo 12

111301 - ReCo 30

111228 - ReCo 51

What credit card and expiry date should we be testing with?

Only pre-approved 'test card' numbers provided by Payment Express can be used for testing, within test environments. We recommend using the test card 111111 for Visa, 111111 for MasterCard, 11114 for Amex, and 0008 for Diners. These can be used with any current expiry, and are suitable only for Payment Express test accounts.