I'm building an integrated payment form with SagePay, and have previously been successful making payments to a test account using the test card details provided in page 24 of this documentation:
However, when I try and pay again with card details in that list that have previously worked, the SagePay form highlights the card number field in red and says "The Card Range not supported by the system."
I've asked the admin of this particular SagePay test account to check if any card ranges have been automatically banned, or something to that affect. Until I get a response, is there anything else that I could be looking out for?
Check which environment you are using.
If you're pointing to the live.sagepay endpoint then test cards will not work and will return the error you've mentioned.
Similar results when you try and use an active card on the test.sagepay.